Symposium FF03—Building Advanced Materials via Particle-Based Crystallization and Self-Assembly of Molecules with Aggregation-Induced Emission

Mesoporous silica based materials and their derivatives in the bulk, as films, and as nanoparticles have attracted a lot of attention for their application potential across different areas, e.g. in catalysis, energy, and nanomedicine. Extensive research efforts have resulted in the continuous discovery of new structures, from quasycristalline to hierarchical structures. Among these materials, cage-type silica mesoporous materials are of particular interest for their facile pore accessibility and versatile functionalization opportunities. The formation of these advanced materials derives from the self-assembly of silica nanocages as the building blocks, following a cage-based crystallization mechanism. However, fundamental understanding of how order emerges on the way from a single cage to a 3D bulk material remains limited.
We recently developed a series of low-dimensional silica structures, with in particular the discovery of isolated pentagonal dodecahedral silica cages formed around single surfactant micelles [1,2]. Dodecahedral cages constitutes the elementary building blocks in a large variety of naturally occurring and synthetic materials, including DNA and RNA cages, clathrates as well as mesoporous silica. These motifs are thus found across a wide range of length scales, in organic as well as inorganic materials. We therefore saw in this discovery an opportunity to investigate the early stages of the growth mechanisms at play in micelle directed self-assembly processes that lead to the formation of cage-type mesoporous silica with well-defined crystallographic structures.
Following a similar strategy as for the formation of nanocrystals superlattices, we assembled silica cages at an interface between two immiscible solvents. By carefully varying the synthesis conditions, we could assemble 2D superlattices with high control over the morphology, going from monolayers to multilayers of cages. While in a monolayer with honeycomb structure the silica cages do not show any orientational order relative to each other, this orientational correlation increases with increasing layer number leading to complex clathrate type structures in silica cage multilayers. Expanding the superlattices beyond 3-4 layers of cages further evidenced a relaxation of the 2D confinement, driving the assembly towards more favorable bulk structures. Thus, with this approach we can observe the emergence of the crystallographic registry as a result of the concerted self-assembly of surfactant micelles directing the silica 3D network.
Since these 2D superlattices can be coherently fabricated over macroscopic film dimensions, the resulting membranes may be of interest for a number of applications. By adopting concepts from 2D electronic materials, tuning the structure, composition and angle between heterostacks of silica cage superlattices is now paving the road for the design of advanced functional and hierarchical superstructures, with potential separation or catalytic properties not accessible via conventional bulk material syntheses.

References:
[1] K. Ma, Y. Gong, T. Aubert, M. Z. Turker, T. Kao, P. C. Doerschuk, U. Wiesner, Nature 2018, 558, 577.
[2] K. Ma, K. A. Spoth, Y. Cong, D. Zhang, T. Aubert, M. Z. Turker, L. F. Kourkoutis, E. Mendes, U. Wiesner, J. Am. Chem. Soc. 2018, 140, 17343.

Hematite with its high earth-abundance and low biotoxicity is considered to be one of the most promising candidates as a catalytic substrate in various new energy devices. In particular, controlling hematite morphology to expose certain high-energy facets appears to be a promising route to performance improvements. In this study, we describe additive-free synthesis protocols that yield diverse uniform nanoparticle morphologies by controlling the concentration of iron ions and hydrothermal temperatures. Increasing the concentration of iron ions and decreasing the hydrothermal temperature was found to systematically inhibit growth along the c-axis and facilitate growth along the b-axis, leading to the formation of bipyramids with {111} facets. Hematite nanostrings were achieved by the assembly of nanocubes with {104} facets and a secondary growth process. Growth by nanoparticle aggregation was investigated in detail sing powder X-ray diffraction (pXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and atomic force microscopy (AFM). These findings may pave the way to production of chemically pure and morphologically well-defined hematite nanoparticles, and to economically advance their practical application in energy devices.

Water adsorption and thin water film formation on unsupported metal oxide nanoparticles can lead to structural and microstructural transformations that arise from different processes like water-assisted self-assembly of particles or dissolution/ recrystallization processes. This presentation deals with examples where structure-property relationships have been established for MgO nanocubes and their transformation behavior in different water containing environments. We will show that water vapor can induce the self-organization of the nanocubes into regularly staggered one-dimensional structures.[1] The transformation evolves via an initial alignment of the MgO cubes, the formation of intermediate elongated Mg(OH)₂ structures, and their annealing induced reconversion into 1-D structures. In the presence of water vapor the particles spontaneously orient themselves to form staggered MgO nanocube assemblies, where the cubes are offset from each other. Ab initio Density Functional Theory (DFT) modelling identifies surface energy changes associated with the cube surface hydration and hydroxylation to promote the uncommon particle assembly.[2] It will be shown how simple process steps like water adsorption via the gas phase or dissolution-recrystallization processes in condensed water can be utilized as valuable routes to generate anisotropic mesostructures. The here presented transformation mechanisms occurring inside and outside an aqueous bulk solution may pave novel routes for inducing texture in ceramics. Moreover, they point to a great test bed for new surface science concepts where the emergence of associated local structures can accommodate important new functionalities which are beneficial for catalytic activity and microstructure evolution.
[1] G.R. Bourret and O. Diwald, J. Mater. Res. 34, 428-441, 2019.
[2] D. Thomele et al. Angew. Chem. Int. Ed. 56, 1407-1410, 2017.

Fe(III)-(oxyhydr)oxide nanocrystals are an emerging basis for cost-effective catalytic substrates, as well as a dominant class of reactive minerals in soils and sediments. In both contexts, developing a molecular-level understanding of crystallization processes that control particle phase, size, and morphology is critical. However, in aqueous solutions near ambient conditions this remains complicated by the challenge of following rapid initial precipitation, yielding the poorly crystalline metastable phase ferrihydrite (Fh), and then the slower mass transfer pathways transforming it into more stable nanocrystals such as lepidocrocite (Lp), goethite (Gt), and hematite (Hm). The slowness of the latter is linked to both the low aqueous solubility of Fe(III), which restricts the dissolution/reprecipitation pathway, and the low solid-state diffusivity of lattice iron, which restricts the topotactic pathway. Particle-based assembly has been proposed in some cases, but alone this cannot accomplish transformation without also recruiting one or both of these two slow pathways. Importantly, addition of only micromolar concentrations of Fe(II) accelerates phase progression by several orders of magnitude.
Here we overview new observations that help unveil principles governing pathway selection and rate, and the catalytic effect of Fe(II). We report a comprehensive experimental/computational study of Fh transformation into Lp/Gt nanocrystals at circumneutral pH, with and without aqueous Fe(II), resolved at the iron site occupancy level. In the absence of added Fe(II), Fh aged over two years was periodically characterized using in situ mXRD with detailed line shape analysis, electron microscopy, and synchrotron Fe L-edge and O K-edge XAS/XMCD spectroscopy quantitatively analyzed using MRCI ab initio calculations. The results are compared to DFT calculations of relative phase stabilities and activation energies for solid-state diffusion of iron along topotactic channels. Tetrahedral Fe(III) is clearly resolved minor component of freshly precipitated Fh, diminishing concomitantly with increasing octahedral Fe(III) and decreasing net magnetic moment until the first appearance of Lp and Gt nanocrystals at ~100 d. Calculated iron diffusion activation energies although as low as 1 eV per unit cell are still too high to support topotactic transformation. Microscopic characterization is well aligned with dissolution/reprecipitation; no compelling evidence for particle-mediated transformation was found. In the presence of Fe(II), an observed ~1000x rate acceleration appears to arise from facile interfacial electron and iron atom exchange that effectively increases the activity of labile Fe(III) at Fh surfaces, resulting in rapid nucleation of Lp and Gt nanocrystal products. Both non-redox and Fe(II)-catalyzed transformation therefore can be explained on a uniform footing via dissolution/reprecipitation. The collective findings suggest the importance of transient Fe(III) species stabilized at interfaces controlling the kinetics of transformation and, in turn, nanocrystal outcomes.

Clay minerals like montmorillonite (MMT), composed of highly anisotropic layers less than one nanometer thick and up to microns wide, are the most abundant inorganic nanomaterials on earth. Particles comprise negatively charged MMT layers separated by discrete molecular layers of water and solvated cations, creating a porous matrix that controls the fate of water, carbon dioxide, nutrients, and pollutants in myriad natural settings. Here, we show evidence of highly dynamic and coupled interactions between clay layers that are accessible through thermal fluctuations, which lead to unexpected particle arrangements and pore structures that are not predicted by current theories.

Stacks of layers exhibit aspects of plastic crystallinity in which the barriers to rotation of an individual layer are on the order of 0-5 kT per unit cell. This results in size-dependent short-range order between neighboring layers whose persistence length depends on the hydration energy of the interlayer cation and its concentration in solution. In the presence mixed electrolytes, particles phase-separate into compositionally distinct particles with different hydration states. A free energy difference of approximately 4 kT per unit cell allows two populations to reach metastable equilibrium through the exchange of both cations and MMT layers. These dynamically rearranging particles exhibit a panoply of topological defects that contribute to the hierarchical structuring of particle aggregates. Non-ergodic evolution of the system dynamics over time produces new structures that continuously emerge over timescales spanning many orders of magnitude. This new perspective on the dynamic structure of MMT reveals potentially general aspects of colloidal interactions in layered materials, and will help improve predictions of ion exchange and fluid transport and retention in many natural systems.

We report a quantum dot-sized organic dot with aggregation-induced emission (AIE) characteristics as a promising cell tracker for noninvasive long-term tracking of adipose-derived stem cells (ADSCs) in living mice. We demonstrate that the AIE dots possess high fluorescence, strong photobleaching resistance, low in vivo toxicity, excellent retention in living ADSCs and negligible interference on the ADSC pluripotency and secretome. The AIE dots also exhibit far superior in vitro cell tracking capability as compared to the widely used commercial cell trackers of PKH26 and Qtracker 655. The in vivo studies using an ischemic hind limb-bearing mouse model reveal that the AIE dots can precisely and quantitatively report the fate of ADSCs and their therapeutic effect in vivo for 6 weeks.
Moreover, we have also synthesized a far-red/near-infrared fluorescent AIEgen-based nanodot, which can efficiently generate reactive oxygen species (ROS) under light irradiation. It is found that the AIEgen-based nanodots are able to visualize tumor tissues and assess tumor margins during surgery in a tumor-bearing mouse model. More importantly, upon tumor removal followed by irradiation of the incision site with light, the AIE nanodots in the residual tumors will generate ROS, which has been demonstrated to successfully suppress the residual tumors and reduce the risk of tumor recurrence after debulking surgery.

Two-dimensional (2D) materials have attracted intense interest due to their unique structures and novel properties for applications in molecular separation, sensing, catalysis, and biomedicine. Despite the unique advantage of the 2D nanostructure in development of functional optical crystals, 2D nanomaterials, such as graphene, graphene oxide and transition metal dichalcogenides, have limited intrinsic optical properties and surface chemistries that restrict them as efficient optical crystals for applications. For example, none them have been directly used as probes for single particle tracking within biological systems.

We recently developed a new class of highly stable and self-repairing 2D nanomembranes (2DNMs)^1,2 from sequence-defined peptoids—a type of protein-mimetic that was invented to mimic the recognition capability of proteins and peptides. These free-standing 2DNMs are highly stable and exhibit a number of properties associated with cell membranes, including thicknesses in the 3.5 - 5.6 nm range, spontaneous assembly at interfaces, and the ability to self-repair. We further demonstrated that a broad range of functional groups can be incorporated and patterned within 2DNMs through large side-chain diversity and/or co-crystallization approaches. In this presentation, I will present our recent progress in the design and synthesis of fluorescent 2D nanocrystals by self-assembly of sheet-forming peptoids conjugated dye molecules. We demonstrated a fine tuning of optical properties of these 2D nanocrystals by varying the dye density and chemistry. The high crystallinity of these 2DNMs enabled a long-range ordering of dye molecules within 2D crystals to achieve unique optical properties, such as high photostability and quantum yield, for applications in biological imaging and molecular sensing.

References
(1) Jin, H.; Jiao, F.; Daily, M. D.; Chen, Y.; Yan, F.; Ding, Y.-H.; Zhang, X.; Robertson, E. J.; Baer, M. D.; Chen, C.-L. Highly stable and self-repairing membrane-mimetic 2D nanomaterials assembled from lipid-like peptoids. Nat. Commun. 2016, 12252.
(2) Jiao, F.; Chen, Y.; Jin, H.; He, P.; Chen, C.-L.; De Yoreo, J. J. Self-repair and patterning of 2D membrane-like peptoid materials. Adv. Funct. Mater. 2016, 8960-8967.

Fluorophores probes are widely used in fields of bioimaging in cells, tissues, or animals and monitoring multiple biological processes in the complex environments. Such sensitive imaging properties allow scientists to make a direct visualization of pathological events and cellular targets. Conventional fluorescent molecules have developed for several decades and achieved great successes, however, their emissions are often weakened or quenched at high concentration or in aggregate state that might result from aggregation-caused quenching (ACQ) effect and reduce the efficiencies of their applications.
In contrast to ACQ effect, aggregation-induced emission (AIE) molecules exhibit strong fluorescence in aggregated states and possess various advantages such as low background, high sensitivity and accuracy, long-term tracking ability, and strong resistance to photo-bleaching. Therefore, those AIE fluorophores are employed as unique fluorescence molecules and excellent modular blocks for the biosensing applications in the field of ions, amino acid, carbohydrates, DNA/RNAs, peptide/proteins, cellular organelles, cancer cells and bacteria.

Aggregation-induced emission luminogens (AIEgens) have attracted concentrated attention in bioimaging due to large stokes shift, fine biocompatibility and good photobleaching resistance. Recently, AIE nanoparticles, as a brand new anti-cancer treatment, can simultaneously achieve dual functions of tumor imaging and treatment, which are promising for clinical medicine. Herein, we successfully co-assembled AIEgens with an antitumor paclitaxel to form Co-NPs for cell imaging and antineoplastic activity. Besides, self-assembly nanostructured AIE photosensitizers with red light emission and high fluorescence quantum yield were prepared for photodynamic therapy. Furthermore, in order to investigate the relationship between molecular structure and photosensitization, we designed and synthesized two types of AIE photosensitizers (PSs) with asymmetrical Donor(D)-Acceptor(A) structure and symmetric A-D-A structure. We found that the singlet oxygen yield could get double promotion by the A-D-A molecule design. It suggested that the designed materials were promising as PSs for potential clinical applications.
Reference
1. H. W. Kun, S. Zhang, J. Y. Qian, J. X. Zhang, X. H. Wang, Z. G. Xie, B. Xu, Y. Q. Han, W. J. Tian, Chem. Asian J., 2019, 14, 1745 – 1753.
2. S. J. Liu, H. K. Zhang, Y. Y. Li, J. K. Liu, L. L. Du, M. Chen, R. T. K. Kwok, J. W. Y. Lam, D. L. Phillips, B. Z. Tang, Angew. Chem., 2018, 130, 15409 –15413.
3. F. Hu, S. D. Xu, B. Liu, Adv. Mater., 2018, 1801350.

In this presentation, ways to harness the powers of enamines will be described. Different stabilized enamines have been developed and applied to configurational switching, metal coordination, and constitutional dynamics through transamination. By controlling the dynamic features, turn-on luminescence effects could be obtained both on the molecular level and when applied to materials. The results show that controllable, enamine-based materials show potential for sensing and imaging applications.

Controlling the emission color of AIEgens is very promising in creating functional luminescent materials. This is usually achieved by modifying the chemical structure of the AIEgens, which is very complicated and are often not very efficient. We show that by attaching a coordinating moiety to the AIEgen, multiple emission can be achieved by simply changing the coordinated metal ions. The metal coordination may bring up changes to (1) the conformation of the AIEgen;(2) the energy gap between HOMO and LUMO of the coordinating AIE molecule; (3) binding affinity to different chemicals. As a result, the emission color and the function of the AIE molecule can be facilely tuned by variation of the coordinating metal ions. Compared to organic synthesis, the coordination strategy is very facile and efficient. We show that by using coordinating AIEgen, we are able to obtain tunable emission and achieve one-on-multiple recognition of important chemicals.

Design of organic molecules exhibiting emission in the aggregated state is increasingly getting attention in the field of materials chemistry. Self assembly of low-molecular-weight gelators (LMWGs) in a particular solvent environment leads to the formation of luminescent gels with 3D nanostructures. Similarly, particular way of stacking by small organic molecules leads to solid state emission. If the self-assembling organogels/small molecules bear hydrophobic alkyl chains, it could be possible to develop superhydrophobic surfaces through self-assembly. Further, self-assembling systems can exhibit mechano responsive switchable fluorescence in solid state, which has wide applications in optoelectronics, sensors, memory chips and security papers. Herein, we present the synthesis and characterization of solid state emitting phenothiazine based organogel linked with poly (alkyl ether) dendron (S1) and small molecule connected with pyridine ring (S2). The hydrophobic alkyl chain present in S1 was effectively utilized to fabricate the superhydrophobic surface with a water contact angle of 157°. Further, small molecule S2 displayed a special kind of mechanofluorochromism (MFC) from cyan blue (480 nm) to green emission (535 nm) with an unusual crystal-to-crystal phase transitions. Upon photoexcitation, S1 and S2 exhibited twisted intramolecular charge transfer (TICT) and aggregation induced blue shifted emission. Further, single point energy calculations using Density functional theory (DFT) authenticate the MFC behavior of S1 and S2. The details of the work will be presented.

While in situ atomic force microscopy (AFM) studies have traditionally focused on nanoscale topographic or mechanical characterization, additional information would greatly benefit in situ studies of biocompatible devices, complex hierarchical materials and energy materials to name a few. Here we present the development of atomic force microscopy modalities for in situ and in operando electrical, electrochemical, and electromechanical studies with nanometer resolution at the electrified solid-electrolyte interface. This work builds on the recent development of an insulated nanoelectrode probe with small active Pt apex, which enables high resolution studies, as shown in the simultaneous acquisition of local EC and conductivity information at electrified solid/liquid interfaces of nanoparticle-catalysed photoelectrodes for water splitting. [1, 2] The range of in situ characterization is further expanded with the new Data Cube AFM modes which provide hyperspectral data comprising voltage and surface distance spectra at every pixel of the image. In particular, Data Cube SECM mode records an approach curve at every pixel thus aiding quantitative modeling of SECM signals. Further, we will show that the variable surface dwell time enables nanocontact EC studies such as local surface EC potential measurement. [3, 4] In general, Data Cube electrical modes provide comprehensive data for ex situ and in situ studies, and the opportunity to extract new kinds of maps through physical modeling of the point spectra or algorithms such as principal component analysis.

Finally, we will present in situ studies of bio-electromechanics with piezo force microscopy (PFM). Despite great interest for biomedical applications, such studies have so far been few other than pioneering work by Kalinin et al. [6, 7] and few other groups. [8] Challenges include the need for chemical compatibility, presence of parasitic electrochemical reactions, capacitive charging from electrical double layers, and de-localized electric field in conductive liquid environments, making the use of physiological conditions impractical. We will show that the use of the nanoelectrode probe mitigates these factors enabling acquisition of PFM data in conductive liquid. [9, 10] Here the use of Data Cube PFM mode not only provides added information about the contact resonance, it also provides higher sensitivity, pushing the PFM detection limit to higher ionic strength.

[1] Nellist et al., Nanotechnology 2017, 28, 095711
[2] Jiang et al., ChemSusChem 2017, 10, 4657
[3] Nellist et al., Nat. Energy 2018, 3, 46
[4] Toma, Nat. Energy 2018, 3, 6
[6] Balke et al. Phys. Rev. Lett. 2006, 96, 237602
[7] Balke et al. ACS Nano 2012, 6, 5559
[8] Giridharagopal et al. Nat. Mater. 2017, 16, 737
[9] Cui et al. Nanotechnology 2019, 30, 235701
[10] Cui et al. Phys Rev Applied 2019, 11, 054037

Among biomolecular composites in nature, the macromolecular-inorganic hybrid biomaterials, like bone, enamel and nacre, have the outstanding physical and biological properties. Several artificial bio-composts with the programmed macromolecular-inorganic interfaces, which are inspired by the native ones, have been reported. However, the in-situ visualizations of the synthesizing/assembly processes, with spatial resolution in nanoscale and temporal resolution in second are still rare. That makes the entropy term and kinetic possibilities are inaccessible in many cases. Hence, the dynamic information in the design and synthesis is often ignored.
In this talk, I will present the in-situ study of the evolution of 2D protein matrixes (DHR-micaN)¹, on the mica surface by in-situ high-speed atomic force microscopy. By tuning the electrolyte type, protein concentration, protein size and intra-protein interactions, the protein molecules can stay as the isolated monomers, condensed liquid, and the anisotropic 2D liquid crystal with smectic order. At [KCl] above 1M, the order develops from an initial 2D liquid phase through the formation of fluctuating clusters. The mica substrate also has certain role to confine the protein nanostructures aligning along pre-defined direction. Those findings have not been previously recorded, and 2D liquid crystal with smectic order had been considered as a non-existent phase in some theoretical analyses. Numerous lines of evidence imply that, besides the programmed protein-mica and protein-protein interactions, the entropic interactions, like the release of interfacial water from the surface and the proteins, also play a critical role in the assembly process.

¹ Baker, et al., Nature in press 2019.

Assembly of 2D patterns on crystal surfaces has been widely investigated to reveal the structural and energetic relationships between the substrate and overlying architecture. Progress has been achieved in understanding and controlling their assembly, yet little is known about the mechanism by which they nucleate. Understanding the dominant pathways and formation kinetics would enable precise control over phase and morphology during synthesis of 2D materials. In our study, short peptides were selected for their ability to bind on MoS₂ (0001). We studied nucleation and growth of 2D films of these peptides directly with in situ AFM and compared our results to molecular dynamics simulations. We find the peptide arrays exhibit an epitaxial relationship to the underlying hexagonal lattice, but assemble row-by-row from dimeric growth along three equivalent directions. The nuclei are ordered from the earliest stages. Although the final crystals are 2D, due to the 1D nature of the constituent rows, there is no critical size, and the nucleation rate varies linearly with concentration and is finite for all concentrations above the solubility limit. Our results verify long-standing but unproven predictions of classical nucleation theory in one dimension while revealing the key interactions responsible for ordered assembly.

The self-assembly of two-dimensional supramolecular networks is a well-known route to control the spatial organization at the nanoscale and beyond as well as bringing new chemical functionality on the surface. With a very few exceptions, these supramolecular networks are, in almost all cases, limited to monolayer thickness. The controlled growth of sequential layers, creating an organic layered structure, has so far been much more limited. Specifically, the additional functional control, which may be achieved through the formation of heterostructures realized by placing one supramolecular layer on another and resulting in growth into the third dimension perpendicular to the substrate, has not been widely explored for these systems.
Here we report on our recent progress in engineering and characterizing organic van der Waals materials – supramolecular heterostructures (SH) with atomic force microscopy (AFM) [1–2]. SHs are layered organic materials that are stabilized by hydrogen bonds in plane and by van der Waals interactions and/or dipolar interactions between layers. They can be formed by, for example, growing sequential layers of bi- and mono-component two-dimensional supramolecular arrays stabilized by hydrogen bonding. The heterostructures are formed on layered materials such as hexagonal boron nitride (hBN), graphite or black phosphorus by depositing layers of cyanuric acid/melamine (CA.M), 1,2,4,5-Tetrakis(4-carboxyphenyl)benzene (TCPB), trimesic acid (TMA) and terephthalyc acid (TPhA) and other molecules.
AFM has confirmed a clear epitaxial arrangement between the layers of the heterostructure, although each layer can exhibit distinct symmetries, for example hexagonal (CA.M) and TMA, square (TCPP), linear (TPhA), rhombic (TCPB) arrangements.
We analyze SHs under ambient conditions using Cypher AFM and demonstrate the routine acquisition of images with 0.1 nm resolution.
The work will present examples of single molecule and sub-molecular resolution. In the latter case, we will discuss the opportunities and challenges in achieving and interpreting ultrahigh resolution AFM images of molecules in the ambient for the purpose of their unambiguous identification.

[1] V. Korolkov et al., Nature Chemistry 9, 1191–1197 (2017)
[2] V. Korolkov et al., Nature Communications 8, 1385 (2017)

Zinc oxide (ZnO) is of much interest for optical applications such as green phosphor, photocatalyst, sunscreen ingredient and transparent electrode. Recently, the photochromic (PC) transition of ZnO nanoparticle induced by UV excitation was reported [1]. The PC transition was confirmed by a reversible change in color depth induced with light irradiation and heat treatment. The purpose of this study is to clarify the microscopic changes of ZnO nanoparticles in association with PC transition. It is concluded that the PC transition occurs for a non-equilibrium crystal phase of ZnO nanoparticles.

The film of ZnO nanoparticles were synthesized by using VHF Plasma CVD. It was exposed to UV lights and annealed at various temperatures to confirm the PC transition. The local atomic environment around Zn atoms were investigated by XANES and EXAFS at Zn K-edge.

The as grown ZnO nanoparticles were transparent. The optical absorption edge did not change with UV irradiation and heat treatment, indicating that ZnO nanoparticles had a Wurtzite structure. The PC states certainly retained below 420 K. At 570 K, however, the color was bleached, it never became darker by UV irradiation. The interatomic distance of Zn nanoparticles was longer than that of ZnO powder as a standard reference: 0.11 Å for Zn-O and 0.02 Å for Zn-Zn. The most interesting structure was observed in Zn-Zn. The coordination number and Debye-Waller factor of PC ZnO were abnormally different from non-PC ZnO.
The absorption edge energy (E₀) of PC ZnO shifted to a lower energy side by heat treatment. The total energy shift was 9.0 eV. The E₀ and the local atomic structure also significantly changed between 420 K and 570 K. Therefore, it is most plausible to consider that a PC ZnO is in a non-equilibrium phase in terms of crystal structure and it likely transforms to an equilibrium phase by heat treatment at 570 K. That is, at least, two kinds of structural phase of ZnO should exist: one is a non-equilibrium structure and the other is an equilibrium one. It was confirmed that the transition from PC ZnO to non-PC ZnO accompanied valence shift and structural changes.
The XANES absorption edge is sensitive to valence states. In the case of mixed-valent manganates and phase mixtures, Mn²⁺, Mn³⁺, and Mn⁴⁺ were clearly determined by the shift of Mn-K absorption edge. The energy shift was 10 eV between Mn²⁺ and Mn⁴⁺. Since the electronic circumstances are different between ZnO and manganates, it is not straight to determine the Zn valence in the same way as manganates.
The Zn valence in ZnO powder is 2. At least, it could be claimed that the Zn valence increased to 2+δ under UV irradiation.

Photochromic ZnO nanoparticles were synthesized by using VHF plasma enhanced CVD. The changes in Zn valence and local atomic structures were investigated by XANES and EXAFS. The absorption edge energy (E₀) and the local atomic structure significantly changed under UV irradiation and heat treatment. The Zn valence of PC ZnO was 2+δ. The coordination number N and Debye-Waller factor σ² of PC ZnO retained under heat treatment at 420K; at 570 K, N and σ² drastically changed and PC ZnO transformed to non-PC ZnO. The transition from PC ZnO to non-PC ZnO accompanied valence shift and structural changes. It was concluded that PC ZnO has a non-equilibrium phase in terms of crystallinity.

This research was supported by the ALCA and A-STEP programs of Japan Science and Technology Agency. This research was partially supported by JSPS KAKENHI Grant Number JP15K04603 and JP26390098. A part of this work was performed under the Cooperative Research Program of "Network Joint Research Center for Materials and Devices”. X-ray measurements were done at Kyushu Synchrotron Light Research Center.

[1] H. Kajiyama et al., “VHF Plasma CVD Synthesis of Photochromic ZnO Nanoparticle”, MRS Adv., http://dx.doi.org/10.1557/adv.2019.80

The creation of an ultra-dense, highly periodic nanoparticle array from a soft building block is one of the most important issues in the fields of material science and nanotechnology. To date, ordered structure made from block copolymer (BCP) have been primarily used as templates for fabricating highly periodic nanoparticle arrays with high areal densities. Herein, we demonstrate for the first time the use of a supramolecular dendrimer assembly for the formation of a highly ordered nanoparticle array with a high areal density of ~20 Tdot/in², four times larger than that of the currently reported BCP-based nanoparticle arrays. By the simple thermal annealing of a supramolecular dendrimers containing a metal precursor between two flat, solid substrates, a hexagonal array of small gold nanoparticles (with a diameter of ~1.6 nm and center-to-center distance of ~5.3 nm), oriented normal to the bottom, was achieved. Density functional theory calculations demonstrated that the gold cation strongly bound with high binding energy to the head group of the dendrimer with a tapered shape. This structure served as a building block for self-assembly into a stable cylindrical structure. The findings obtained in this study provide a new paradigm for creating highly periodic, ultra-dense nanoparticle arrays by using a supramolecular assembly. It is important to note that we studied only one dendrimer, which possessed a hexagonal cylindrical structure, while numerous other dendrimer materials, which have a large diversity in terms of phase, size, and chemistry, exist in nature. We anticipate that this study will lead to the creation of a large family of supramolecular dendrimers that can be utilized as soft templates for creating periodic, ultra-dense nanoparticle arrays.

Up to date, nanostructured Ti-based materials have attracted considerable attention due to their unique and diverse physico-chemical properties and potential for diverse applications. Among them, nanostructured potassium (K) incorporated Ti-based oxide materials (KTiO_x) have received particular attention due to their wide range of interesting applications, e.g. in photovoltaic cells, batteries, photochromic and electrochromic devices, photocatalysis, gas sensors, biomaterials, owing to their remarkable structural and physical properties. However, so far one of the main bottlenecks for diverse applications has been the nanostructures fabrication, which generally involves complicated process, low reproducibility and high cost for chemical modification. Since the physical properties can be greatly affected by the size and morphology of the nanostructures as well as the precise incorporated K amount, several processes had to be combined, exacerbating these drawbacks. This drawback strongly limits their fast implementation in potential applications. Hence, elaborating a process that allows easy synthesis and a simple tuning of the desired morphology and properties via a single-step process is currently one of the key issues in this research field.
We used the wet corrosion process (WCP) which was developed in my previous research to Ti metal plates. In this work, we extended our studies to different Ti-based metal substrates and systematically investigated, for the first time, the characteristics of the resulting KTiO_x depending on the initial Ti content prior to WCP. The results clearly indicate direct correlation of the nanostructures fabrication with the Ti content in the initial material. Moreover, optical properties of the KTiO_x could be correlated with their structural properties. Understanding the direct relationship between the Ti content of the initial metal and the condition of WCP to control the structural and physical properties makes it possible to produce the KTiO_x on demand, for various applications.
Ti-based materials are currently considered as one of the most promising candidates for multifunctional semiconductor photocatalysts. We have investigated the photocatalytic performance of KTiO_x fabricated by WCP. This result can be very interesting for photoinduced catalysis.
We fabricated nanostructured KTiO_x via WCP using the Ti, TAV, and TN substrates. Systematically the relation between the Ti content of the initial metal and the condition of WCP was studied, with the conclusion that these parameters strongly control the morphology and physical properties of the generated nanostructures. One-dimensional nanostructures could be obtained within a specific window of the process condition: Ti and TAV metals which contain more than 90% Ti yielded elongated nanostructures of K-incorporated titanium oxide after treatment with 10–20 mol/L-KOH solution. In contrast, TN metal with about 50% of Ti content required a KOH treatment with >20 mol/L-KOH solution indicating that the process window shifted to higher concentration. For all samples the morphology evolution as a function of the WCP condition was similar, but the precise Ti content of the initial material determined the amount of incorporated potassium as well as the KOH concentration at which elongated nanostructures were produced. In detail, we focused on Ti series to estimate the photocatalysis application. Structural and crystalline properties of KTiOx were studied by means of X-ray diffraction, scanning and transmission electron microscopy. Chemical composition was determined by X-ray fluorescence and energy-dispersive X-ray analysis. Photocatalytic performance was investigated by studying the degradation of methylene blue, cardiogreen, and azorubine red dyes upon UV irradiation. The negatively charged crystalline KTiOx nanostructures with high surface area showed significantly higher photocatalytic degradation compared to their KTiOx counterpart.

Mesocrystals consisting of assemblies of smaller crystallites have received much attention because of their crystallization pathway beyond classical theory and emergent functionalities that are not present in the individual components. Of various materials, magnetite (Fe₃O₄) exhibiting soft magnetism has been extensively studied and utilized broadly in electronics and biomedicine for decades. Because the magnetic properties of Fe₃O₄ mesocrystals depend on the crystallite and particle sizes, it is necessary to understand how they are determined during the crystallization process. However, the crystallization mechanism of Fe₃O₄ has been addressed phenomenologically by observing just a part of the entire crystallization pathway; thus, the details of the crystallization mode remain unclear.
In this study, we suggest that nonclassical and classical pathways are concurrently involved in the formation of clustered mesocrystalline Fe₃O₄ nanoparticles (c-Fe₃O₄ NPs), and the microstructure is affected by which pathway governs the reaction overall. We note that different ferric (oxyhydr)oxide polymorphs appear separately as intermediates on each pathway and can be chemically controlled. In early stages of the reaction, we observe a nonclassical pathway on which c-Fe₃O₄ NPs grow by oriented attachment of primary particles that form directly from lepidocrocite. In a late stage of the reaction, we observe a classical pathway on which Fe₃O₄ NPs form by stepwise transformation of lepidocrocite, goethite, and Fe₃O₄, in that order. We present the kinetics of each pathway as a Johnson–Mehl–Avrami–Kolmogoroff (JMAK) model that describes the isothermal transformation process. Based on this understanding, we can control the diameter and crystallite size of c- Fe₃O₄ NPs independently according to the content ratio of chemicals in a broad range. Finally, we report successful experimental implementation of the crystallite size effect on the coercivity curves as a function of diameter. Because c-Fe₃O₄ NPs represent a crystallographically ordered aggregate of spheres, we can discuss the collective coercivity behaviour, which is hard to observe in single NPs.

Simple, scalable and inexpensive method for the synthesis of metal oxide thin films is highly demanded for the emerging applications especially in the field of sensing and nanoelectronics. We demonstrate an effective method for synthesizing polycrystalline thin films of metal oxides using a unique reaction design at the air−liquid interface. We have exploited this interface reaction design to synthesize SnO₂ and PdO thin films and engineered their properties by varying the reaction parameters. These free-standing sheets have been synthesized by one step hydrothermal reaction at the interface with surfactant-free method. The thin films formed at the interface have a lateral dimension in centimeter. A possible growth mechanism is proposed. The metal oxide particles formed in the bulk of the solution move to the interface and get trapped to form a continuous, polycrystalline film to minimize the energy of the system. Transmission Electron Microscopy (TEM) has been basically used to understand self-assembly of the particles. TEM study shows that the films are formed due to the self-assembly of oxide nanoparticles (~30 nm in size) trapped at the interface; hence are polycrystalline. X-ray diffraction, Scanning Electron Microscopy and Atomic Force Microscopy measurements have been carried out to understand the structure, morphology and thickness of the films. These films are highly stable at elevated temperatures. The properties of these thin films can be manipulated simply by changing the reactant concentration and other reaction parameters like temperature and time of reaction. We have explored thickness tunability by varying the precursor concentration which in turn affects optical and electronic properties; hence the sensing behavior. SnO₂ films showed astounding gas sensing performance towards H₂S by demonstrating 25 ppb (S = 19.3%) as the lowest limit of detection at 150°C. The sensor can operate reliably in the range of 25 ppb to 6 ppm (S=25621%) H₂S. H₂S is known to be exhaled in “Bad Breath” (also known as Halitosis). It is considered as “normal” in the range of 80–160 parts-per-billion (ppb), “weak” in the range of 160–250 ppb, and “strong” if exhaled in concentrations greater than 250 ppb. Hence, sub-ppm detection of H₂S can aid in disease diagnosis at early stage. The highly sensitive and selective detection of this sensor makes it a potential candidate for breath-based diagnostics. This class of materials synthesized in two-dimensional morphology is extremely interesting for fundamental studies as well.

Monoclinic β-Ga₂O₃, which has a direct wide bandgap (Eg = 4.9 eV at room temperature), has tremendous potential as an electronic device material due to its excellent physicochemical properties including chemical stability, high mechanical properties, and thermal stability. In particular, the high breakdown voltage of monoclinic β-Ga₂O₃ and its transparency in the visible light region are suggesting promising applications in many fields such as power semiconductor, electromagnetic wave shielding, ultraviolet shielding agents, gas sensors, field effect transistors, and solar cells. In previous studies, monoclinic β-Ga₂O₃ was used as a single crystalline wafer grown by the edge-defined film-fed growth (EFG) method, and as a form of thin film fabricated by various vacuum deposition methods such as magnetron sputtering, pulsed laser deposition (PLD), molecular beam epitaxy (MBE), metal-organic vapor phase epitaxy (MOVPE), metal-organic chemical vapor deposition (MOCVD) and sol-gel method. However, the EFG method can obtain β-Ga2O3 with high purity, but it requires a lot of energy in the process. β-Ga₂O₃ in the form of the thin film can be manufactured with a precise pattern, but it has disadvantages that require high-vacuum deposition equipment. These two traditional approaches have limitations on the extended use of monoclinic β-Ga₂O₃.
Recently, as the 3D printing technology in the metal and polymer fields has developed remarkably, it has brought innovation in the manufacturing field. For example, airplane parts made with powder bed fusion (PBF) type 3D printing technology can be manufactured in a lightweight structure that could not be manufactured by conventional methods. This allowed us to improve fuel efficiency and profitability.
In our work, the process screening platform was established for the fabrication of 3D hierarchical structured monoclinic β-Ga₂O₃ using customized PBF-type 3D printer. We also developed the controlled process management system by facilitating process variables including the viscosity of β-Ga₂O₃ paste, one-step layered thickness, laser experimental conditions (power, scan direction, scan speed), and atmospheric condition. The sintering behavior of nano-sized β-Ga₂O₃ particles and hierarchical structure evolution of β-Ga₂O₃ layers were investigated. The analytical results (XRD, XPS, UV-vis absorbance, surface roughness, domain size, etc.) revealed that higher sintering activity led to the increased densification reaction resulting in lager domain size and fewer contents of the pore. Establishment of the optimization process of monoclinic β-Ga₂O₃ manufacturing by our laser sintering method ensures promising adaptability of PBF type 3D printing technology for ceramic materials.

This abstract reports a new method that cotton textile modified with bismuth nanoparticle can block x-ray radiation effectively within hundreds of micro-meter thickness. Bismuth nanoparticle is grafted on the nanocellulose which is a bridge to crosslink nanoparticle on the textile. The homogenous dispersion of nanoparticles on textile fiber surface is attributed to this spatially distributed modification, which enhances the shielding efficiency to 90% for 500 mm nanoparticle modified cotton textile. The fact that the relationship between shielding rate and thickness agrees well with the Beer-Lambert law, facilitates the prediction of shielding rate in specific application. Given its low cost, light weight, structure conformability and wearability, bismuth nanoparticle modified cotton textile will find its use in a wide range of fields related to personal radiation protection.

YBO3:Eu crystals with flower-like hierarchitecture are readily synthesized through a folic acid assisted hydrothermal process using polyborate precursors in the aqueous solution. It was found that the pH value , borate/yittrium ratio and the mass of folic acid take effects on the morphology and photoluminescence emission intensity of YBO3:Eu crystals .The product with the small flower-like hierarchitecture was obtained under the conditions of pH value at 9, borate/yittrium ratio at 2 and the mass of folic acid at 0.44g, showing the strongest photoluminescence intensity. Such a hydrothermal route using folic acid as a capping agent may provide a green and effective method for fabricating useful and complex 3D architectures of LEDs phosphors.

Polymer nanocomposites containing small fractions of nanoparticles (NPs) have the ability to produce materials with higher mechanical properties due to the combination of properties of the inorganic NPs (e.g., stiffness, thermal stability) and polymer (e.g., flexibility, ductility and processability). The mechanical properties of these nanocomposites are linked to the dispersion of NPs in the matrix. Thus, an excellent dispersion of the nanoparticles is the main hindrance in the processing of nanocomposites. One of the most promising strategy for overcoming this challenge is the use of self-assembly (SA) of hybrid structures, as macromolecules grafted on NPs, providing a simple and rapid method for constructing orderly structures with several degrees of complexity[1]. On the other hand, despite the progress in controlling the equilibrium structure of grafted NPs, these nanocomposites exhibit a low tensile strength fragility that limits the control of physical properties over macroscopic areas. This behavior is even more critical for nanocomposites with high quantity of NPs. In face of this scenario, this study aims to provide fundamental insights into the hybrid structures as a building blocks for new materials with tailored physicochemical properties, notoriously with high ratio hybrid structures/polymer matrix. Based on this, Polyethylene Glycol (PEG) at different molecular weights (PEG Mw = 3000 and PEG Mw = 6000) was used as grafting polymer on Magnetite (Fe₃O₄) NPs, which were synthesized in a single step-route[2]. By improving organic interactions within the hybrid structures, thin films samples with superior mechanical behavior were produced by controlled evaporation of the grafted NPs colloid, consolidation by uniaxial pressure and mild thermal treatment. All these steps were analyzed by Scanning Electron Microscopy (SEM) (F50 Inspect) and Transmission Electron Microscopy (Tecnai F20), where it was possible identify the myriad of hybrid structures organization, interactions and fracture behavior. The films were also characterized by dynamic mechanical test, and through the data was possible to get some insights into the relationship of storage modulus and loss modulus with NPs size, shape, PEG density on the surface of NPs, PEG chain size, and interactions between NPs-PEG/PEG-NPs. Then, this study demonstrates the potential of hybrid structures as building block for the development of advanced materials by correlating fundamental mechanical behavior with structure assembly and the interaction within the organic grafted molecules.

1. Dreyer, A., et al., Organically linked iron oxide nanoparticle supercrystals with exceptional isotropic mechanical properties. Nature Materials, 2016. 15(5): p. 522-+.
2. Goncalves, R. H., C.A. Cardoso, and E.R. Leite, Synthesis of colloidal magnetite nanocrystals using high molecular weight solvent. Journal of Materials Chemistry, 2010. 20(6): p.1167-1172.

Solid-state light, such as light-emitting diodes, organic light-emitting semiconductors, polymer light-emitting diodes, etc., have the advantages of small size, high luminous efficiency and long life, which are used to replace traditional lighting sources. Nakamura Shuji, Isamu Akasaki and Hiroshi Amano won the 2015 Nobel Prize for their high-efficiency Light Emitting Diode (LED). In a short period of time, LED lighting has developed into a lighting source with a market penetration rate of 31%. The market size of China alone has reached more than 200 billion yuan. However, LED has certain limitations as an illumination source. The problem of “efficiency drop” has always limited the wide application of white LEDs.
In these years, the emergence of laser diode (LD) technology has further expanded the types of new lighting sources. Compared with the LED light source, the LD light source has the following characteristics: (1) The electro-optical conversion efficiency is high. In the work of An Zhenfeng et al. [6], an LD component with an efficiency of 71% is prepared by optimizing the device structure, and usually LED The electro-optical conversion efficiency is generally about 20%; (2) the volume is smaller, the volume of the LD component is usually one percent of the LED component, and has greater advantages in terms of weight reduction and design; (3) the LD light source does not There is a problem of "significant efficiency drop", and the device operation is not unstable due to working time and operating temperature. Therefore, LD light source instead of or auxiliary LED light source is expected to become a new direction of solid-state light source developmen.
When the LD light source is used as a white light illumination source, it is also necessary to refer to the synthesis method of the white LED light source. The commonly used methods include two categories: (1) the three primary color method (three primary color method), and the so-called three primary color method refers to the use of red, green, and blue. The LD light source of the same color emits light at the same time, and the three colors are mixed to obtain white light ; (2) the fluorescence conversion method, the LD light is irradiated on the material having photoluminescence property, and the emitted fluorescence is mixed with the original light of the light source. After getting white light. Usually use ultraviolet or blue light as the excitation source, and yellow and red phosphors as the fluorescent material.
Fluorescence conversion method is more advantageous in terms of cost and safety, and is more suitable for production as an industrial product. Therefore, the preparation of LD device by fluorescence conversion method has become a hot spot for research and enterprise development. However, most of the fluorescent conversion materials used in current laser illumination devices contain rare earth metals, which are costly and limit the further application of laser illumination devices.
In our work, a fluorescent polymer with Aggregation-Induced Emission (AIE) is prepared as a fluorescent conversion material, and the effects of different processes on its light conversion effect are explored. Controlled emission from cyan to red can be achieved through pH regulation, which is based on the principle that pH can effectively control spatial conjugate by altering the aggregation of carboxylic acid groups and hydroxyl groups The results show that using this material as a fluorescent conversion material, white light is produced after blue laser excitation, its CIE 1931 coordinates (0.365,0.335), color temperature 4177K, belongs to the neutral white area. which is expected to replace the existing fluorescent materials for semiconductor lasers.

Recently, the spherical photonic crystal called a photonic ball has attracted attention [1-4]. It consists of the primary structure, which is a periodic array of colloidal particles, and the secondary structure of the spherical shape. The wavelength of reflection exhibits the red shift when the primary particles become large. An interesting optical property has been reported for photonic balls with colloidal particles larger than 350 nm[1]: a ring-shaped iridescent reflection can be confirmed on the peripheral region of the photonic ball when observed using an optical microscope. On the other hand, photonic balls macroscopically have a specific color when observed by the naked eyes, despite the iridescence observed under the microscope.
The reflection mechanism of the peripheral region is divided into two opinions; one is the grating diffraction which originates from regularly arranged colloidal particles on the surface of the photonic ball [2, 3], and the other is Bragg diffraction caused by lattice planes of the face-centered cubic (fcc) [4]. The former idea can explain the iridescent reflection, but not the specific color when observed with the naked eye. However, the latter idea explains the specific color only.
Further, the reflection on the peripheral region does not form a perfect ring; there are non-reflective dark regions. The areas of the non-reflecting regions largely depend on the numerical aperture of the objective lens. With the numerical aperture increase, the reflective areas expand. For example, using an objective with the numerical aperture 0.90, the non-reflecting area disappears, and the complete ring-like reflection appears on the peripheral region.
In this study, we propose a theoretical model to explain the above complicated optical properties of the photonic ball. In this model, the reflection of Bragg diffraction by the fcc lattice planes coexists with the reflection of the grating diffraction that consists of surface particles [5]. It is confirmed that the wavelength fulfilling the interference condition of Bragg diffraction of the (220) planes simultaneously satisfies that of the grating diffraction. In addition, detailed observations with optical and electron microscopes revealed a distinctive structural difference between the reflective and non-reflective regions: the in-plane arrangement of colloidal particles on the surface is different with respect to the radial direction of the ball between the two regions. From detailed experiments and theoretical calculations, we have found that the non-reflective region does reflect light, but into a highly oblique direction which cannot be observed under the optical microscope using the objective lens with a low numerical aperture.
We have also investigated the angular dependence of the reflection, and found that the photonic ball exhibits very low iridescence macroscopically. This is because of the unique reflection mechanism where both the Bragg and diffraction grating are important. From this low iridescence, the photonic ball can be a suitable candidate for the structurally colored pigment.

References
[1] Y. Zhao et al., Acc. Chem. Res., 2014, 47, 3632.
[2] N. Vogel et al., Proc. Natl. Acad. Sci. USA, 2015, 112, 10845.
[3] V. Rastogi et al., Adv. Mater., 2008, 20, 4263.
[4] S.-H. Kim et al, J. Am. Chem. Soc., 2008, 130, 6040.
[5] R. Ohnuki et al., Adv. Optical Mater., 2019, DOI: 10.1002/adom.201900227.

Nowadays, most of aggregation-induced emission luminogens (AIEgens) with donor (D) - acceptor (A) structures are based on propeller-shaped triphenylamine (TPA) as electron donor. After years of development, TPA-fused AIEgens are comprehensively developed with hundreds of papers published in past few years. Although there're many similarity between phenothiazine and TPA, AIEgens based on phenothiazine is much fewer than TPA based AIEgens. In this contribution, we designed and synthesized 11 PTZ derivatives through Knoevenagel Condensation. Almost all the PTZ dyes are emissive at red spectral region, above 600 nm. In addition, PTZ10 and 11 were found emissive at the NIR region with high fluorescecne quatum yield in the solid state (~5 %). Since PTZ doesn't have any rotatable elements like normal AIEgens, we investigated the exact driving force for the AIE behaviour of the PTZ dyes through quantum mechanics computation and single crystal analysis, from which the restriction of intramolecular vibration was proved to be the AIE mechanism. Moreover, we used PTZ6 which has fairly a high fluorescence quantum yield (~20 %), to selectively track the lipid droplets of HeLa cells with vert high contrast, demonstratig a high application potential of the PTZ dyes.

Aggregation-induced emission (AIE) is a photophysical phenomenon correlated closely with the excited state intramolecular motions e.g. rotation and vibration. Although AIE has attracted increasing attention due to their significant applications in biomedical and optoelectronics, an in-depth understanding of the excited state intramolecular motion and elucidation of the origin of the intramolecular motion are yet to be fully developed. Here we found that the non-aromatic annulene derivative of cyclooctatetrathiophene (COTh) shows typical AIE phenomenon in spite of its rotor-free structure. The underlying mechanism was systematically investigated through photoluminescence (PL) spectra, time-resolved absorption spectra, theoretical calculations, circular dichroism (CD) and circular polarized luminescence (CPL) spectroscopy as well as by pressure-dependent fluorescent spectra, which indicated that the aromaticity reversal from ground state to the excited state served as a driving force for inducing the excited state intramolecular vibration, leading to the AIE phenomenon. To our knowledge, this is the first time that aromaticity reversal is demonstrated as a reliable strategy to develop novel vibronic AIE systems. And this work also provides a new viewpoint to understand the excited state intramolecular motion behavior of lumiongens.

Recently, a new aggregation-induced emission (AIE) system with anion-π⁺ interactions was first developed and demonstrated a novel strategy to develop inherent-charged AIE luminogens (AIEgens). AIEgens with charges possess unique advantages, such as enhanced biocompatibility and subcellular targeting ability resulted from electrostatic interactions between biomacromolecules and AIEgens. Therefore, they are expected to find wide biological applications. Unfortunately, the introduction of charges to AIEgens often suffers from complicated synthetic route, tedious purification and low yield. Herein, a new AIEgen, namely TTPABQ, with anion-π⁺ interactions was designed and obtained via one-pot synthesis. TTPABQ possesses a high specificity to bacteria and high photostability. It can image both Gram-positive and negative bacteria in a wash-free manner. This greatly simplify the imaging process. Furthermore, TTPABQ can also work as a promising photosensitizer to kill bacteria through efficient generation of reactive oxygen species upon white light irradiation.

Multifunctional nanomaterials integrating the prominent feature of each single functional moiety offer a great potential in multimodality tumor imaging and synergistic treatment. The traditional strategy for achieving multifunctional nanoplatforms adopting one-by-one combination of different constituents, suffers from the problems of complicated structural design, sophisticated purification and natural incompatibility between several functionalities. Herein, a novel “less is more” strategy is presented to realize multifunctionality within a simple silver core/AIE (aggregation-induced emission) shell nanoparticle. Surprisingly, apart from their intrinsic AIE fluorescence (FL) and noble-metal based computed tomography (CT) properties, an extra interface with excellent photothermal (PT) and photoacoustic (PA) functions was in situ generated between the core and shell part. As a result, multifunctional nanoparticles integrated with FL, PA, CT, radiotherapy (RT) and photothermal therapy (PTT) properties were achieved and performed excellently in correlated tumor imaging and synergistic therapy.

Development of polymerization methodology to afford polymers with unique structures and advanced functionalities is of considerable academic significance and technological implication. Among various multicomponent reactions, the A³-coupling of aldehyde, alkyne and amine has been established as a convenient and atom-economical method to construct nitrogen-containing heterocycles. To construct novel functional polymers with well-defined structure, our group has been working on the exploration of polymerization methodology from alkyne monomers for decades. However, there is still a plenty room for improvement. For example, the development of metal-free polymerizations is highly desirable due to the high cost and biological toxicity of metal catalyst residues. It is hence desirable to develop metal-free efficient polymerization of alkynes to avoid such problems.
Herein, a facile and highly efficient approach towards functionalized polyquinolines was designed and developed by formic acid-catalyzed multicomponent polymerizations of alkynes, arylamines and glyoxylates. Conjugated polyquinolines were formed in situ with high molecular weights (M_w up to 16 900) in nearly quantitative yields (up to 97.5%). Fluorescence tunable polyquinolines were achieved by altering the electron-donating substituents of the alkyne derivatives. The incorporation of luminogens into the polymer backbone rendered the resulting polymers with various aggregation-induced fluorescence behaviors. The tetraphenylethene-containing polyquinolines demonstrated to be a sensitive and highly selective fluorescence sensor of Cr(VI). Compared to other metal ions including K⁺, Na⁺, Mg²⁺, Ca²⁺, Al³⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Pb²⁺, Ag²⁺, Cd²⁺, Hg²⁺ and Cr³⁺, the fluorescent sensing of Cr(VI) was more specific with an emission quenching ratio of over 20-fold. After a series of mechanism studies, the fluorescence quenching effect of Cr(VI) was proved to induced by inner filter effect. Such a non-irradiation energy conversion manner ensured the flexible and straightforward technique for the detection of Cr(VI).

In clinical studies, thiol measurement in the whole blood is of diagnostic and prognostic significance. In addition, the detection of mitochondrial thiol is very important for investigating cellular functions or /dysfunctions. Here, a ratiometric aggregation-induced emission luminogen (AIEgen) called TPE-PBP for thiol detection was developed by introducing a para-dinitrophenoxy benzyl pyridinium moiety to tetraphenylethylene. TPE-PBP exhibits excellent biocompatibility, high photostability, and large two-photon absorption cross-section. TPE-PBP emits red fluorescence in PBS buffer without thiol. Upon addition of thiol, there is a gradual blue shift of TPE-PBP’s emission with ratiometric fluorescent response because of cleavage of the dinitrophenyl ether bond by thiol followed by the self-immolation of the para-hydroxybenzyl moiety to produce a less-conjugated AIEgen. The in vitro quantification of thiol is enabled by the linear ratiometric fluorescence response with a very low limit of detection. Considering the high sensitivity and good selectivity towards thiol detection, TPE-PBP was also utilized to detect thiol in the blood. Furthermore, mitochondrial thiol in vitro, ex vivo and in vivo were quantitatively mapped by TPE-PBP using fluorescence microscopy under one- and two-photon conditions.

Purely organic luminogens with thermally activated delayed fluorescence (TADF) can harvest singlet and triplet excitons to afford high electroluminescence (EL) efficiencies for OLEDs. However, most TADF emitters have to be dispersed in host matrix to prevent aggregation-caused quenching (ACQ). The doped OLEDs of TADF emitters often encounter a knotty problem of severe efficiency roll-off as luminance increases, which defers practical application of TADF emitters in industry. In our group, we are working on the luminogens with aggregation-induced emission (AIE), which are free of ACQ. Recently, we develop a series of novel luminogens with aggregation-induced delayed fluorescence (AIDF), which can facilely solve the aggregation-caused emission quenching and/or exciton annihilation problems of current TADF emitters. They are composed by an electron-withdrawing carbonyl core and various electron-donating groups, such as phenoxazine, phenothiazine, 9,9-dimethyl-9,10-dihydroacridine, carbazole and so on. They exhibit weak emissions without delayed fluorescence in solutions but strong emissions with prominent delayed components upon aggregate formation or in neat films, exhibiting the typical AIDF characteristics. The nondoped OLEDs based on the neat films of these AIDF luminogens exhibit lowered turn-on voltages and increased luminance (> 100000 cd m^-2) with respect to the doped OLEDs. Thanks to the excellent exciton utilization (~100%), the nondoped devices furnish remarkable EL efficiencies of up to 72.9 cd A^-1, 81.8 lm W^-1 and 22.6%, and negligible efficiency roll-off at 1000 cd m^-2.^[1-4] To the best of our knowledge, these devices are the most efficient and stable nondoped OLEDs reported so far.

References

1. Liu, H.; Zeng, J.; Guo, J.; Nie, H.; Zhao, Z.; Tang, B. Z. Angew. Chem. Int. Ed. 57, 9290 (2018).
2. Huang, J.; Nie, H.; Zeng, J.; Zhuang, Z.; Gan, S.; Cai, Y.; Guo, J.; Zhao, Z.; Tang B. Z. Angew. Chem. Int. Ed. 56, 12971 (2017).
3. Guo, J.; Li, X.-L.; Nie, H.; Luo, W.; Gan, S.; Hu, S.; Hu, R.; Qin, A.; Zhao, Z.; Su, S.-J.; Tang, B. Z. Adv. Funct. Mater. 27, 1606458 (2017).
4. Guo, J.; Li, X.-L.; Nie, H.; Luo, W.; Hu, R.; Qin, A.; Zhao, Z.; Su, S.-J.; Tang, B. Z. Chem. Mater. 29, 3623 (2017).

Benefiting from high aggregated-state emission, superior photostability and low cytotoxicity, a various of AIE luminogens (AIEgens) have been designed as fluorescent bioprobes for cell imaging. The entry process of AIEgens into cells has been rarely investigated although it is of fundamental importance. Herein halogen-labeled AIEgens with specific organelle targeting properties have been comprehensively designed for tracking their entry process into cell and their distribution inside the cells. Cooperatively with confocal fluorescent imaging, the techniques of time of flight secondary ion mass spectrometry (ToF-SIMS) have been applied to analyze the distribution of AIEgens during the process of bioimaging. This study will not only provide new strategies for designing biofunctional AIEgens but also bring new insight for understanding the cell entry process of AIEgens.

LED with narrow full-with at half maximum (FWHM) has been studied to realize natural color mimetic displays. Due to relatively broad FWHM of organic-LEDs, perovskites have been suggested as an alternative. Even though perovskites have narrow FWHM, low stability hindered the usage of perovskites in LED fields. Color filters, such as photonic crystals, have been applied to narrowing the FWHM of emitting light based on the optical resonance at the edge of the photonic bandgap. However, angle-dependency of the photonic bandgap has been a big obstacle that should be overcome. Herein, organic-inorganic hybrid perovskite-embedded copolymer particles are prepared via self-emulsion polymerization (SEP) to increase the stability of the perovskite and improve the angle-dependency of the photonic bandgap. PbBr₂-embedded copolymer particles firstly prepared then the particles are self-assembled to polycrystalline photonic crystals. The embedded precursors are converted to perovskite using vapor-assisted solution process (VASP). The stability of the perovskite was enhanced due to the encapsulating polymers. Photoluminescence intensity increased ~12% and FWHM of the emission narrow down to ~13 nm due to the resonance effect of the photonic bandgap. Moreover, angle-dependency of photonic bandgap has been improved due to the polycrystalline structure of photonic crystals.

The development of organic room temperature phosphorescent (RTP) materials is accompanied by opportunities and challenges. The relationship between polymorphisms and RTP properties has attracted much attention as the different molecular packings of one molecule in solid state, which exhibits significant different optical and electronic properties. Herein, we report an organic molecule BBP-BO with unique polymorphic emission properties. Two kinds of BBP-BO crystals were obtained, crystal A exhibit bright photoluminescence (PL) with a quantum yield of 11.25%, which is higher than that of crystal B (6.85%). Interestingly, Crystal A shows a distinct RTP phenomenon with a long lifetime of 17.92 ms@492 nm, but Crystal B has a relatively weak RTP phenomenon with short lifetime of 3.49 ms@492 nm. Crystal structures analysis shows that the different optical properties of the two crystals are related to the molecular packing mode. The further exploration how molecular packing affect RTP property is essential for designing and synthesizing novel RTP materials.

Better understanding of the mechanism of aggregation-induced emission can help develop novel AIE systems and exploit novel applications. Here, we have disclosed the microscopy mechanism of AIE by systematically investigating the excited-state electronic transition property, nuclear vibrational modes, the radiative and nonradiative decay rate constants, and the fluorescence quantum efficiency using the thermal vibration correlation function rate theory coupled with quantum chemistry calculations.[1] For typical AIEgens with the nature of (π, π*), we have put forward that the block of the nonradiative decay channels recovered strong emission in aggregate.[2] The nonradiative decay channels refer to the molecular vibration modes with large electron-vibration coupling value. We have found the rotational, twisting, bending and stretching vibration modes can be largely restricted in aggregate, resulting in the decrease of the nonradiative decay rate. For some hetero-AIEgens, we have proposed that the conversion from dipole-forbidden (n, π*) or (σ, π*) state to dipole-allowed (π, π*) state happen to induce strong emission when going from solution to aggregate. [3] Then, we have proposed some strategies to probe and verify the mechanism using the resonant Raman spectrum, isotopic effect, pressure effect, and the nanoparticle size effect and so on. Some of them have been fully confirmed by the experiments. Furthermore, the molecular design principles are raised and many unusual AIE fluophors are designed theoretically and synthesized experimentally. [4]

References:
[1] Z. Shuai, Q. Peng, Natl. Sci. Rev. 4, 224 (2017); Z. Shuai, Q. Peng, Phys. Reports, 537, 123 (2014); Q. Peng, Y. Niu, Q. Shi, X. Gao, Z. Shuai, J. Chem. Theory. Comput., 9, 1132 (2013).
[2] Q. Peng, Y. Yi, Z. Shuai, J. Shao, J. Am. Chem. Soc. 129, 9333-9339 (2007); T. Zhang, Y. Jiang, Y. L. Niu, Q. Peng, Z. Shuai, J. Phys. Chem. A, 118, 9094 (2014).
[3] H. Ma, W. Shi, J. Ren, W. Li, Q. Peng, Z. Shuai, J. Phys. Chem. Lett. 7, 2893 (2016);
P. A. Yin, X. G. Gu, Z. M. Wang, Q. Peng, Submitted to J. Phys. Chem. Lett. (2019); H. Ma, Q. Peng, Z. An, W. Huang, Z. Shuai, J. Am. Chem. Soc., 141, 1010 (2019)
[4] T. Zhang, Q. Peng, C. Quan, H. Nie, Y. Niu, Y. Xie, Z. Zhao, B. Tang, Z. Shuai, Chem. Sci., 7, 5573 (2016); F. Bu, R. Duan, Y. Xie, Y. Yi, Q. Peng, R. Hu, A. Qin, Z. Zhao, B. Tang, Angew. Chem. Int. Ed., 54, 14492 (2015); T. Zhang, H. Ma, Y. Niu, W. Li, D. Wang, Q. Peng, Z. Shuai, W. Liang, J. Phys. Chem. C, 119, 5040 (2015); X. Zheng, Q. Peng, L. Zhu, Y. Xie, X. Huang, Z. Shuai, Nanoscale, 8, 15173(2016); W. Zhao, Z. He, Q. Peng, J. Lam, H. Ma, Z. Qiu, Y. Chen, Z. Zhao, Z. Shuai, Y. Dong, B. Tang, Nat. Commun. 9, 3044 (2018); T. Zhang, W. Shi, D. Wang, S. Zhuo, Q. Peng, Z. Shuai, J. Mater. Chem. C, 7, 1388, (2019)

Every year a huge volume of electronic wastes (e-waste) are being discarded with an increasing trend due to the technological and scientific advancements. To many countries, this kind of waste is to be a major concern since various kind of materials including metals (basic and pernicious metals), polymers and ceramics are entangled elaborately and too hard to be separated readily. PCBs are considered as one of the main splits of e-wastes containing around 35% metals. The metallic portion includes Cu, Zn, Ni, Sn and Fe, making this waste stream valuable as a secondary source of raw materials after separation and purification. In this research, we focused on the metallic portion of waste PCBs to turn them into value-added nano-materials practical application including nano-fluids, wastewater purification and water splitting. The projects step is as below:
1. In the first step, we focused on presenting a feasible and novel process to enhance the amount and purity of metallic portion of the waste PCBs without further chemical or/and physical. Two milling stages including knife mill and ring mill were applied to increase the liberation degree followed by a physical flotation process using bromoform fluid for beneficiation and enrichment. To recognize the composition and metal content in each classification, the classified (using sieve shaker) powders were characterized in each stage. Eventually, the mixture of all powder was characterized in term of its thermal behavior and composition of exhausting gas to estimate its threat for the environment.
2. In this step, we used the classified waste PCBs as a source of initial alloying powders to synthesis a homogenous nano-structured Cu-Zn-Sn-Fe-Ni alloy via mechanical alloying. This nano-structured powder is commonly used in a range of applications where the heat transfer and conductivity play a vital role such as nanofluids or additive manufacturing. To characterize the properties of powders, various characterization methods were utilized including XRD, XPS, FESEM, EDS, HRTEM, STEM, UV–Vis and optical microscopy. Finally, as a potential application, a nanofluid solution was prepared and characterized using pH and conductivity measurements.
3. In the next step, we tried to leach all remaining metals to a solution just in one leaching step using HNO₃. One of the objectives of this stage was to minimize the leaching time, amount of acid applied and energy consumption. To achieve these targets, a multi-variant multi-response statistical method was used to optimize the leaching efficiency of major metals content. Lastly, to understand the composition and importance of the residue, the solid residue of leaching was characterized.
4. In this stage, SnO₂ quantum dots were unexpectedly formed as spontaneous precipitation with a very slow kinetic rate from the last step leaching solution. The precipitation was triggered without the use of any chemicals or surfactants. It also occurred selectively as a by-product without influencing the solubility of other metal-containing ionic species. Then, the precipitation mechanism in the solution and the measurement of the surface area and other characteristics of the QDs were identified. After calcination, the SnO₂ QDs were applied to wastewater treatment to remove methylene blue (MB) as dye pollution.
5. In the last step, the solution containing Cu²⁺, Zn²⁺, Ni²⁺, Al³⁺, and Pb²⁺ ions was exposed to three ion exchange resins (Amberlite IRA 743, Lewatit TP 208 and Lewatit TP 260) to extract and separate the metallic ions of heavy metals. In addition to the optimization of resin load, contact time and solution temperature, the thermodynamics and kinetics of the adsorption were calculated to prove the accuracy and reliability of the experiments. The preferred locations of adsorbed ions on resin beads were traced and analyzed by electron microscopy. Finally, a stripping process was applied to examine the desorption selectivity and enhance recycling efficiency.

Chiral cage compounds are important because they exhibit extending functions such as chiral recognition and circularly polarized luminescence. Generally, two strategies have been established to construct chiral cages: by using chiral precursors, or based on the chirality at metal centers. Inspired by mathematics, we have reported a strategy to generate emergent chirality of organic cages by assembling achiral two-dimensional truxene building blocks into chiral octahedra through dynamic imine chemistry.
Tetraphenylethylene (TPE) and Pentaphenylpyrrole (PPP) are well-known aggregation-induced emission chromophores (AIEgen) and exhibits two rotational patterns in its propeller-like P or M configurations, respectively. Through dynamic covalent chemistry, the chiral molecular Face-Rotating Polyhedra (FRP) were constructed from restricting phenyl flipping of TPE or PPP. Accompanied by the generation of chirality, strong fluorescence also emerged during cage formation. In the study of FRP, we provide the strategies to predict the shape of FRP and the number of isomers. This study provides insight into construct chiral cages by the rational design through graph theory, and might facilitate further design of cages and other supramolecular assemblies from aggregation-induced emission active building blocks.

Chiral tetraphenylethylene (TPE) derivatives, as well known AIE chromophores, have great potential in chiral recognition and circularly polarized luminescence. However, they were mainly constructed through introducing chiral substituents at the periphery of the TPE moiety, which required additional chemical modifications and limited the variety of chiralities of products. We constructed a series of chiral face-rotating sandwich structures (FRSs) through restricting the phenyl flipping of TPE without introducing any chiral substituents. In FRSs, the TPE motifs display P or M configuration which resulted in complex pattern arrangements and a variety of chiralities. Interestingly, only four isomers, as two pairs of enantiomers, were found in the assemble system and two of them are thermodynamic products. And we also found that non-covalent repulsive interactions in vertices caused the facial hetero-directionality of FRSs, and the hydrogen bonds between imine bonds and hydroxy groups induced excited-state intramolecular proton transfer (ESIPT) emission of FRSs. In addition, the fluorescence intensity of FRSs decreases with the addition of trifluoroacetic acid. Our study provides new insights into the rational design of chiral assemblies by means of AIEgens, such as TPE and its derivatives, through restriction of intramolecular rotation (RIR), which can be applied in luminescent materials, chiral molecular recognition or asymmetric catalysis.

Reference
1. Mei, J.; Leung, N. -L.; Kwok, R. -T.; Lam, J. -W.; Tang, B.-Z. * Chem. Rev., 2015, 115, 11718
2. Qu, H.; Tang, X.; Wang, X.-C.; Li, Z.-H.; Huang, Z.-Y; Zhang, H.; Tian, Z.-Q.; Cao, X.-Y.* Chem. Sci., 2018, 9, 8814

Previously it was shown that molecular imprinting (MI) technology can be used to produce biosensors with the potential for use in point-of-care diagnostics for detection of Zika virus, pancreatic cancer, polio and other antigens, etc. [1]. MI biosensors utilize a self assembling monolayer (SAM) of hydroxy-terminated alkanethiol chains on gold-coated silicon chips. The SAM crystallizes around the target analyte. Once crystallized, the monolayer retains the shape of the analyte allowing it to sensitively and selectively bind the target analyte. The analyte is measured using a simple potentiometric readout. These sensors are easy to implement and only require a simple potentiometer for detection. Hence they can be especially useful in third world areas where advanced sensing instrumentation is lacking. The sensor chips require sterile laboratory conditions for imprinting, but they can be used at point of care, which may be remotely located. In order to reach these areas, it is important to optimize the method of storage and shipping the imprinted detector.
MI sensors were fabricated as previously described [1] using hemoglobin as the target analyte and incubated at room temperature in the desiccator for up to a week while our control chips were tested fresh, without incubation. Following 72 hours of incubation, MI biosensor detected the analyte (hemoglobin) with almost no loss of sensitivity as compared to freshly prepared control sensors. However by 120 hours of incubation the biosensor no longer demonstrated a linear response to increasing concentrations of target analyte indicating that the SAM was unstable under test conditions. These data suggest that the thiols used in SAM are sensitive to moisture present under atmospheric conditions, and hence should always be stored in vacuum unless they are used within the day that they are imprinted. It is encouraging that the chips did not show deterioration within the first 72 hours when stored in a rough vacuum, similar to the one used in food storage applications, hence they could be vacuum packed and shipped overnight to the point of care. Further work is in progress to improve the vacuum conditions and extend the lifetime of the chips. .

[1] Y. Wang, Y. Yu, J. Sokolov, K. Levon, and M. Rafailovich, Current Trends in Polymer Science, 18, 1, 2018

Colloidal nanocrystals are promising building blocks for the construction of hierarchical 2D and 3D components for use in optical, electronic, magnetic, and therapeutic devices. Therefore, multiple assembly techniques (e.g., entropic, depletion, electrostatic, biorecognition) have been developed to engineer hard or soft nanoparticle-based crystalline materials. DNA-mediated crystallization, which uses DNA-grafted nanoparticles as “artificial atoms” to generate hierarchically ordered superlattices (e.g. soft colloidal crystals), has advantages over other assembly techniques because the nanoparticle core “atom” identity (nanoparticle size, shape, and composition) can be tuned independently of the DNA “bonds” (sequence, strength, length, and density). However, it still remains a challenge to pattern DNA-functionalized colloidal crystals into specific shapes while retaining crystallinity. Herein, we report on the light-induced patterning of colloidal crystals engineered with DNA. Light-responsive colloidal crystals are synthesized by incorporating azobenzene-tethered DNA as bonding elements. Here, the photo-isomerization of azobenzene molecules between the trans- (visible light) and cis-form (UV light) directly translates into a change in the DNA hybridization interactions, resulting in a reversible switching between nanoparticle binding and non-binding states. We thus utilize such light-controlled assembly and disassembly to selectively remove nanoparticles that are located outside of a desired pattern. Specifically, we assemble a crystalline thin film of DNA-grafted nanoparticles and then apply UV-light to controllably dehybridize certain DNA strands which enables their dissolution leaving behind the desired pattern. The light-responsive printing of DNA-functionalized colloidal crystals marks a significant step towards fabricating advanced “smart materials” that can be dynamically manipulated via different types of stimuli on-cue.

The self-assembly of colloidal nanocrystals (NCs) into superstructures provides an efficient bottom-up pathway for constructing new functional materials. Among various superstructures, NC superlattices represent an entirely new class of solid-state materials with unique collective properties and wide applications. However, conventional NC superlattices are inappropriate structural motifs for energy applications due to the impeded molecular accessibility of NCs by foreign species. In pursuit of widening the range of applications of NC superlattices, it is desirable to develop new architectures that enable full access of NC constituents while simultaneously facilitating mass transport properties. Herein, I will focus on low-dimensional, hierarchical NC superlattices with rationally designed structures and mesoscale morphologies toward high-performance energy storage and conversion. I will also spend half of the time to cover NC superlattice derivatives, especially ordered graphene-like frameworks, which are emerging as a new class of mesoporous carbon materials. By exploiting the versatile surface chemistry and self-assembly behaviors of colloidal NCs, a rich array of mesoporous graphene-based materials can be designed, which show great promise as material platform for energy applications.

Metamaterials exhibiting desirable optical phenomena require the precise assembly of nanoscale building blocks with positional and orientational control. Colloidal crystal engineering with DNA offers the ability to chemically program the structure of nanoparticle-based materials with sub-nanometer precision in three dimensions. This structural control enables the design and discovery of new materials with previously unattainable functionalities and the determination of key structure-property relationships. DNA-programmable assembly can be applied to the field of optical metamaterials to dramatically expand the range of architectures that can be synthesized by chemists and explored by theorists. Through the convergence of bottom-up DNA assembly with top-down lithographic approaches, colloidal plasmonic nanoparticles of different sizes, shapes, and compositions can be precisely placed in two and three dimensions on a surface to form optically active superlattices. Additionally, exploiting DNA’s native responsiveness to chemical stimuli provides dynamically reconfigurable superlattices that are particularly interesting as metamaterials. These large-area superlattices, which would be difficult, if not impossible, to synthesize with any other currently available top-down or bottom-up technique, enable the use of colloidal nanoparticles as metamaterial building blocks and provide a platform to investigate and design new types of light-matter interactions in nanoparticle-based metamaterials.

Crystallization by particle attachment is a widespread phenomenon in synthetic and natural environments. In mineral systems, this process exhibits diverse styles ranging from oriented attachment of like phases to mis-oriented aggregation of disparate phases followed by coarsening to single crystals. While descriptions of these systems must share a commonality with continuum-based DLVO-type theories for simple colloids, mineral systems present additional complexities, including face-specificity of dielectric properties, structured nanoscale interfaces, and solvent-responses of a comparable length scale. To understand the relationship between nanocrystal structure, interparticle forces and assembly dynamics, we are investigating nanocrystal assembly of titanium, iron and zinc oxides. For ferrihydrite (FeOOH) and ZnO, in situ TEM demonstrates that direction-specific forces align diffusing particles prior to contact and that attachment occurs on lattice matched faces via a sudden jump to contact. Direct AFM-based measurements of the forces between both TiO₂ and ZnO surfaces reveal orientation dependent attractive interactions exhibiting the symmetry of the underlying lattice. MD simulations indicate a combination of hydration and dispersion forces orient the particles and that barriers caused by hydration layers, cannot be overcome by simple Brownian forces in the absence of fluctuations of the layers. Classical DFT simulations suggest these barriers are greatly reduced and attractive forces increased through ion correlation interactions. Addition of organic ligands, like oxalate, to the ferrihydrite system produces a dramatically different pathway and outcome: Nanoparticles of hematite (Fe₂O₃) nucleate sporadically from the ferrihydrite and, once formed, are covered with oxalate and drive all new hematite particles to nucleate within about 1 nm of the interface, after which they jump to contact. The oxalate inhibits growth and coarsening of the particles, leading to spindle-shaped aggregates of crystallographically aligned particles with a fixed and constant aspect ratio. Thus the random assembly process seen in the pure ferrihydrite system is replaced with one that is deterministic due to interface-driven nucleation.

We combine top-down fabrication and bottom-up assembly processes to construct artificial, meta-molecules, materials, and devices with unconventional physical properties from colloidal, metal nanocrystal (NC) building blocks. Lithographically-defined, size- and shape-engineered topographical templates are used to direct the capillary assembly of NC metamolecule oligomers. We map the evolution in optical response as we increase the number of nearest neighbor shells in close-packed spherical NC assemblies, and as we construct trimers of nanorods that assemble along the edges of equilateral triangles to form open structures.^1,2 The triangular arrangement of nanorod trimers supports strong magnetic plasmon modes in their open interior, and circumferential displacement of the nanorods generates a chiroptical response under unidirectional oblique illumination. We also combine nanoimprint lithography with solution-based deposition of NCs to form superstructures for large-area, active metamaterials. By chemically exchanging the long ligands used in NC synthesis with more compact ligand chemistries we control interparticle distance.³ This ligand-control of distance allows us to tailor a dielectric-to-metal phase transition seen by a 10¹⁰ range in DC conductivity and a dielectric permittivity ranging from everywhere positive to everywhere negative across the whole range of optical frequencies. We realize a "diluted metal" with optical properties not found in the bulk metal analog, presenting a new axis in plasmonic materials design. Using this approach, we demonstrate strong, near-infrared optical absorbers that transduce light to heat.⁴ We also demonstrate quarter-wave plates with extreme bandwidths and high polarization conversion efficiencies in the near- to-mid infrared.⁵ Finally, we exploit the distinct chemical and mechanical properties of NC assemblies, in comparison to bulk materials, to create 2D, lithographically-defined NC/bulk bimorphs, which upon ligand exchange, transform to create functional 3D architectures.⁶

(1) Greybush, N. J.; Liberal, I.; Malassis, L.; Kikkawa, J. M.; Engheta, N.; Murray, C. B.; Kagan, C. R. Plasmon Resonances in Self-Assembled Two-Dimensional Au Nanocrystal Metamolecules. ACS Nano 2017, 11 (3), 2917–2927.
(2) Greybush, N. J.; Pacheco-Peña, V.; Engheta, N.; Murray, C. B.; Kagan, C. R. Plasmonic Optical and Chiroptical Response of Self-Assembled Au Nanorod Equilateral Trimers. ACS Nano 2019, acsnano.8b07619.
(3) Fafarman, A. T.; Hong, S.-H.; Caglayan, H.; Ye, X.; Diroll, B. T.; Paik, T.; Engheta, N.; Murray, C. B.; Kagan, C. R. Chemically Tailored Dielectric-to-Metal Transition for the Design of Metamaterials from Nanoimprinted Colloidal Nanocrystals. Nano Lett. 2013, 13 (2), 350–357.
(4) Chen, W.; Guo, J.; Zhao, Q.; Gopalan, P.; Fafarman, A. T.; Keller, A.; Zhang, M.; Wu, Y.; Murray, C. B.; Kagan, C. R. Designing Strong Optical Absorbers via Continuous Tuning of Interparticle Interaction in Colloidal Gold Nanocrystal Assemblies. ACS Nano 2019, acsnano.9b02818.
(5) Chen, W.; Tymchenko, M.; Gopalan, P.; Ye, X.; Wu, Y.; Zhang, M.; Murray, C. B.; Alu, A.; Kagan, C. R. Large-Area Nanoimprinted Colloidal Au Nanocrystal-Based Nanoantennas for Ultrathin Polarizing Plasmonic Metasurfaces. Nano Lett. 2015, 15 (8), 5254–5260.
(6) Zhang, M.; Guo, J.; Yu, Y.; Wu, Y.; Yun, H.; Jishkariani, D.; Chen, W.; Greybush, N. J.; Kübel, C.; Stein, A.; et al. 3D Nanofabrication via Chemo-Mechanical Transformation of Nanocrystal/Bulk Heterostructures. Adv. Mater. 2018, 1800233.

Early observation of strong circular dichroism for individual nanoparticles (NPs) and their assemblies have developed into a rapidly expanding field of chiral inorganic nanostructures. The chiral inorganic nanostructures encompass sophisticated constructs from metals, semiconductors, ceramics, and nanocarbons with multiple chiral geometries with characteristic scales from Ångströms to microns. Many of them are formed spontaneously from polydispersed building blocks, which enables their structural and functional engineering over a broad range geometries and optical properties. This talk will address (1) the mechanisms of chirality transfer in inorganic materials, (2) the origin of the uniquely high values of optical anisotropy, (3) the fundamental challenges of multiscale chirality observed in nanostructures, and (4) physicochemical differences/similarities with chiral supramolecular, liquid crystal, and biological systems. The analysis of phase diagrams for the assembly of chiral NPs affords understanding essential role of long-range correlations between NPs and a possibility of critical phenomena in the assembly at nanoscale that can lead to exceptionally complex assemblies from polydispersed nanocomponents exemplified by chiral hedgehog particles. The parallels with biomineralized skeletons of coccoliths help understanding the need for chiral asymmetry in live matter. Simplification of the chiral assembly processes also helps accelerating the development of technologies based on chiroplasmonic, chiroexcitonic, and chiromagnetic effects observed for the individual NPs and their assemblies exemplified by the polarization vision mimicking that of some organisms.

Although one-dimensional nanostructures of ZnO have been suggested to form via oriented attachment (OA), the detailed mechanism underlying this process remains unresolved as no direct observations of ZnO OA have been reported. Here we use in situ liquid phase (LP)-TEM to directly observe and investigate dynamic aspects of ZnO nanorod formation by OA. Detailed analysis on translational and rotational motions of ZnO particles, tracked in real time, demonstrates that aggregation-coalescence via OA event was the primary mode of ZnO particle growth, and in some cases produced chain-like ZnO nanostructures. While the particle interactions with molecular granularity suggest a qualitative difference between ZnO OA and near-OA events, our study shows that the attachment event is notably influenced by dynamic nature associated with the particle motions such as abnormal particle diffusivity and quasi-2D nature under confinement. Our study suggests a complementary aspect to obtain better understanding of the OA, as well as the current viewpoint mainly focusing on energetic considerations.

Nanostructured Zinc oxide (ZnO) has great importance in many areas, such as catalysis, sensors, cosmetics and biomedical applications. In literature, ZnO nanorods (NR) are the most widely studied nanostructure. However, the mechanism of their growth into the final rod-shape is not well understood. In the present work, we have synthesized ZnO NR and studied its temporal growth mechanism, using zinc chloride as a precursor and hexamethylenetetramine (HMTA) as a reducing agent. It has been reported that, HMTA degrades into ammonia and formaldehyde at a certain temperature which subsequently provides hydroxyl ions and helps in the ZnO nanostructure formation. Hence, to understand the role of temperature, NR synthesis has been done at various temperatures, namely 65, 75, and 85 °C. It was observed that, the time required for NR formation decreased with increased in temperature, which was confirmed by nanostructure morphology at different reaction time-points. Length to diameter aspect ratio (AR) of NR is found to vary from ~ 1 to ~ 9, from the initial to final time-point (180 min). It correlates well with using ICP-AES, the utilization of Zn²⁺ ion in NR formation which increases with higher temperature (< 20 %, 20 % and 55 % at 65, 75, and 85 °C respectively at 180 min).

To capture the evolution of ZnO NR formation, intermediate samples were characterized by scanning electron and transmission electron microscopy. Initially, a new crystal structure- a hollow “nanocone” (NC) crystals of ZnO (AR ~1) was observed. Further, these crystals find a perfect crystalline match and self-organize with a neighboring NC, which results in the formation of a binary NC pair. Latter these pairs each grow in 1-D direction only, leading to the hexagonal ZnO NR. The NCs may have high intrinsic surface energy, which makes them find and attach to a similar crystalline surface of another NC, together forming NC pair. We have observed that this NC pair now acts as a base for NR formation because growth is occurring, only at both the ends along the length of the NC. Characterization techniques such as XRD and XPS have been done for analysing crystal size, phase formation and oxidation state respectively, for intermediate products. Synthesized ZnO NRs are presently being used in the degradation of pharmaceutical wastes in water.

Keywords: ZnO, Nanocone, Nanorod

Nanocrystals (NCs) exhibit unique size- and shape-dependent physicochemical properties arising from low dimensional quantum confinement effects and have been successfully used as building blocks for the fabrications of 2- and 3-dimensional NC arrays for the development of ‘artificial solids’ (or metamaterials) with new collective optical and electronic properties derived from the interaction or coupling of different NCs in an assembly. NC surface chemistry plays a key role in control of microstructures of the NC arrays such as mesophase. Here we report our recent progress in development of surfactant-assisted micelle confined noncovalent self-assembly and synthesis of active nanostructures. This approach is simple, general, and can be used to synthesize highly ordered nanostructures with different sizes and shapes. Through using varied surfactants and building blocks, this method provides a unique opportunity for subsequent self-assembly through hydrogen-bonding, π-π stacking, charge interactions, etc. and formation of highly ordered nanocrystal arrays with controlled mesophase, orientation, and material forms (film, powder, particle).
Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Persistent room-temperature phosphorescence (RTP) under ambient conditions is attracting attention due to its strong potential for applications in bioimaging, sensing, or optical recording because materials with persistent RTP can be utilized for high contrast emission imaging independent of autofluorescence using small and cost effective photo-detectors. To extract efficient persistent RTP, the control of the radiative rate from the lowest triplet excited state (T₁) (k_p), the nonradiative rate of intramolecular vibrational relaxation at room temperature (RT) from T₁ (k_nr(RT)), and the triplet quenching rate at RT caused by interactions with the ambient surroundings (k_q(RT)) is crucial. In the last five years, k_nr(RT)+k_q(RT) have been suppressed in a variety of heavy atom-free conjugated crystals under ambient conditions, which has allowed electrons in T₁ to partly access the persistent RTP pathway with small k_p. However, for complex conjugated crystalline systems a key strategy to suppress k_nr(RT) and k_q(RT) as well as increase k_p for the efficient persistent RTP is not found yet.

Here, we investigate electronic structures controlling k_p, k_nr(RT), and k_q(RT) of heavy atom-free conjugated molecular crystals showing persistent RTP. For the analysis of k_q(RT), high resolution optical microscopy analysis showed that, despite a favorable molecular stacking, aromatic crystals with persistent RTP are characterized by small diffusion length and significant small values of the diffusion coefficient of triplet excitons. Quantum chemical calculations reveal a large overlap between the lowest unoccupied molecular orbitals but very small overlap between the highest occupied molecular orbitals (HOMOs). Inefficient electron exchange caused by the small overlap of HOMOs prevents triplet excitons from diffusing over long distances and consequently from quenching at defect sites inside the crystal or at the crystal surface, contributing to minimization of k_q(RT). For k_nr(RT), analysis using vibrational spin–orbit coupling (SOC) at RT indicates that the large decrease of k_nr(RT) hardly decreases before and after crystallization for the heavy atom-free conjugated crystals. Cooperative analysis using the high resolution microscope as well as the quantum chemical calculation indicated that the large decrease of k_nr(RT)+k_q(RT) is caused by not the decrease of k_nr(RT) but the large decrease of k_q(RT) owing to the small diffusion of triplet excitons at RT. For overall electronic structures to access the persistent RTP, the localization of HOMO due to moderate charge transfer (CT) conjugated structure or π-degeneracy of three dimensional highly symmetric conjugated structures might be a key. The HOMO localization sometimes induces moderate CT character in transitions between high-order singlet excited states (S_m) and the ground state (S₀) as well. Stronger SOC between the moderate CT characteristics of the S_m–S₀ transitions and local excited characteristics of the T₁–S₀ transition contribute to the large increase of k_p independent of k_nr(RT).

This is first overall analysis of k_p, k_nr(RT), and k_q(RT) of heavy atom-free conjugated molecular aggregates. This knowledge of electronic characteristics, k_p, k_nr(RT), and k_q(RT) of conjugated molecular crystals will be important for realizing efficient persistent RTP from a variety of conjugated molecular crystals.

Synthetic amphiphilic polymers have been developed since last decades for the purpose of forming self-assembled polymer vesicles (polymersomes) which mimic the structures of lipid vesicles (liposomes) and the properties of cells in some extent. Polymersomes are much more stable, more robust and less permeable than liposomes due to the high molecular weight of polymers. They show high loading capacity for both hydrophobic molecules entrapped in the membrane and hydrophilic ones encapsulated in the inner aqueous compartment. Another interesting feature of polymersomes is that their properties can be finely adjusted by the rich chemical design of the amphiphilic building blocks. Stimuli-activatable functions, fluorescence-generating moieties and targeting groups can be introduced to make smart polymersomes which are currently studied as a means of drug delivery and biomedical imaging.
Our group has focused, since several years, on the tailor-design of smart polymersomes based on biocompatible and biodegradable building blocks. In this communication, I will present fluorescent polymersomes with aggregation-induced emission (AIE), which are made of polycarbonates, polyesters, polyurethanes, and N-substituted poly(amino acid)s containing AIEgens. Some of these AIE polymersomes are also stimuli-activatable and can be opened under CO₂- and pH-stimulation. We aim to develop innovative approaches to cell/tissue imaging and controlled drug delivery with in situ bio-distribution tracing.

References:
[1] Zhang D. P., Fan Y. J., Chen H., Trépout S., Li M.-H. "CO₂-activated reversible transition between polymersomes and micelles with AIE fluorescence", Angew. Chem. Int. Ed., 2019, published on line: https://doi.org/10.1002/anie.201905089.
[2] Chen H., Li M.-H. “Recent Progress in Fluorescent Vesicles with Aggregation-induced Emission”, Chin. J. Poly. Sci., 2019, 37, 352-371.
[3] Zhang D. P., Zhang Y., Fan Y. J., Rager M.-N., Guérineau V., Bouteiller L., Li M-H., Thomas C., "Polymerization of Cyclic Carbamates: A Practical Route to Aliphatic Polyurethanes", Macromolecules, 2019, 527, 2719-2724.
[4] Chen H., Zhou L., Shi X., HU J., Guo J., Albouy P.-A., Li M.-H. “AIE Fluorescent Gelators with Thermo-, Mechano- and Vapo-Chromic Properties”, Chem. Asian J. 2019, 14, 781-788.
[5] Yu X., Chen H., Shi X., Albouy P.-A., Guo J., Hu J., Li M.-H. “Liquid crystal gelators with photo-responsive and AIE properties”, Mater. Chem. Front., 2018, 2, 2245 – 2253.
[6] Deng Y. W., Ling J., Li M.-H. “Physical stimuli-responsive liposomes and polymersomes as drug delivery vehicles based on phase transitions in the membrane”, Nanoscale 2018, 10, 6781 – 6800.
[7] Zhang N., Chen H., Fan Y. J., Zhou L., Trepout S., Guo J., Li M.-H. “Fluorescent polymersomes with aggregation induced emission”, ACS Nano 2018, 12, 4025−4035.

A series of dinuclear Ir( III ) Schiff base complexes have been synthesized and shown to exhibit both aggregation induced emission (AIE) and piezochromic luminescence (PCL) behaviour. We employed highly flexible Schiff base ligands to construct an AIE-active molecule with strong intermolecular interactions between the aryl rings in the aggregated or crystal state. The multifunctional dinuclear Ir(III) complexes are applied in second-level anti-counterfeit trademark, data encryption device and reversible monitoring device for volatile organic compounds.

Covalent Organic Frameworks (COFs) and Metal-Organic Frameworks (MOFs) are versatile porous materials with promising applications in a vast number of fields. Nevertheless, the high temperatures and the hazardous solvents required for the synthesis of these materials, among the poor solubility of the starting building blocks in the reaction media have provided a poor control over the size of the crystalline domains generated and in the morphology of COF/MOF crystals. These factors have limited the processability of COF and MOF hindering the integration in functional devices, as well as preventing their use in bio-systems. Therefore, great efforts are made in the field to understand and control the growth of COF and MOF crystals at length scales spanning from the nano- to the micrometer scale.^1-3 Inspired by the confined spaces employed in living systems to constrain the crystallization processes, here we report for the first time a methodology for preparing stable aqueous colloidal solutions at room temperature of crystalline COF and MOF nanoparticles. This procedure allows downsizing these porous-materials beyond the previously reported limits, being able to, for example, synthesize MIL 100(Fe) nanoparticles under 20 nm. Additionally, thanks to their nanosized shape, we demonstrate the possibility to process these materials into a variety of micro- and millimeter-sized structures. We have demonstrated that by controlling the aggregation of the colloids, two-dimensional freestanding films and three-dimensional shapes can be accomplished. Among to improve their bioavailability, these results will undoubtedly open new possibilities for the implementation of COFs and MOFs into functional devices.

Cyclometalated iridium complexes are of considerable interest due to their high photoluminescence quantum yields (PLQYs) at room temperature, physicochemical stability and long (several microseconds) PL lifetimes leading to their widespread applications in organic light-emitting diodes (OLEDs), as light-emitting electrochemical cells (LECs), biological labels, chemosensors for inorganic ions, data recording and security protection devices.

We will report that efficient Aggregation Induced Phosphorescence Emission (AIPE) of an ionic di-Ir(III) complex occurs when the counterion is exchanged specifically by perchlorate in aqueous media. As a result, a rapid, highly selective “turn-on” phosphorescent response to perchlorate is observed in aqueous media. X-ray crystallography, transmission electron microscopy and theoretical calculations support the photophysical data and the sensing mechanism.[1] We have also synthesized mono-iridium(III) complexes which possess aggregation-induced emission enhancement (AIEE) and detect the explosive 2,4,6-trinitrophenol (TNP) selectively with high quenching constants in aqueous media. The sensing mechanism has been systematically investigated by mass spectrometry, ¹H and ¹⁹F NMR spectroscopy and X-ray crystal structure analysis. A hydrogen bonding interaction between TNP and the ancillary ligand of the Ir complex explains the high selectivity for TNP compared to other nitro-aromatics.[2]

References
[1] Li, G.; Guan, W.; Du, S.; Zhu, D.; Shan, G.; Zhu, X.; Yan, L.; Su, Z.; Bryce, M. R.; Monkman, A. P. Chem. Comm. 2015, 51, 16924.
[2] Che, W.; Li, G.; Liu, X.; Shao, K.; Zhu, D.; Su, Z.; Bryce, M. R. Chem. Comm. 2018, 54, 1730.

To construct π-molecules with different structures is one of the key points in the research field of opto-electronic materials. In many cases, the molecular structure not only affects the intramolecular π-conjugation, but also the intermolecular π-π stacking, to result in the different functionalities. In this talk, some typical examples will be presented to partially demonstrate the interesting different properties with minor or even ignorable structural difference.

References
1. J. Yang, X. Zhen, B. Wang, X. Gao, Z. Ren, J. Wang, Y. Xie, J. Li, Q. Peng, K. Pu, Z. Li, Nature Commun., 2018, 9, 840.
2. Z Chai, M. Wu, M. Fang, S. Wan, T. Xu, R. Tang, Y. Xie, A. Mei, H. Han, Q. Li, Z. Li, Adv. Energy Mater., 2015, 5, 1500846.
3. Y. Xie, Y. Ge, Q. Peng, C. Li, Q. Li, Z. Li, Adv. Mater., 2017, 29, 1606829.
4. R. Tang,; S. Zhou,; Z. Cheng,; G. Yu,; Q. Peng,; H. Zeng,; G. Guo,; Q. Li,; Z. Li, Chem. Sci., 2017, 8, 340.
5. J. Yang, Z. Ren, Z. Xie, C. Wang, Y. Xie, Q. Peng, Z. Chi, Q. Li, Z. Li, Angew. Chem.-Int. Ed., 2017, 56, 880.

Growth of metallic nanowires is of practical importance for manufacturing integrated circuits in semiconductor industries. Copper (Cu) nanowires recently have been considered one of the promising materials in commercial application because of its superior electric/thermal properties. Experimental researches have shown that Cu nanowire growing on amorphous carbon (a-C) substrates is productive, but to our best knowledge the microscopic mechanism of how a-C film morphology affects Cu cluster diffusion remains to be unclear. Our molecular dynamics (MD) simulations of Cu cluster diffusion with a time scale of 300 ns laid down a prior knowledge for nanowire growth engineering, and showed that Cu nanoclusters with diameter of 1 was locally-diffused rather than globally-diffused on a 2.0 g/cm³ a-C film. This suggested that the substrate roughness is crucial to the diffusion behavior. To further clarify the mechanism, we carried out the MD simulations with different cluster sizes, diffusion paths, and surface roughness. Through trajectory analysis of MD simulations, the relation among diffusion coefficients, cluster sizes and surface roughness was built, and showed that increasing surface roughness on a-C film may localize the trajectory of Cu cluster and reduce its size dependence on Cu cluster diffusion. Therefore, our simulation results may draw a new direction in nanowire growth engineering for controlling the diffusion pattern of Cu cluster by tuning the surface roughness of a-C substrate.

I will present a number of examples, in which oriented attachment of nanoscale building blocks rather than atomic deposition is responsible for the formation of noble-metal nanostructures with well-defined and controllable morphologies or shapes. Typical morphologies include nanocubes, wavy nanowires lined with planar defects, and dendritic nanostructures. The key requirement is the formation of a large number of nanoscale building blocks at the very beginning through homogeneous nucleation and the initiation of colloidal stability due to depletion of stabilizer from the surface of the building blocks. Due to the inclusion of planar defects, such nanostructures are attractive catalytic materials for a range of reactions and applications.

A major goal in nanoparticle synthesis is to control nanoparticles with atomic precision and reveal their total structures (i.e., core plus surface ligands). This talk will present some breakthroughs in metal nanoparticle research, including the atomically precise synthesis via solution chemistry and total structure determination by X-ray crystallography, as well as the assembly/crystallization of nanoparticles into hierarchical macroscale structures. By controlling nanoparticles with atomic precision, one can now reveal the long sought-after total structures of nanoparticles at the atomic level, such as the 1 nm Au₂₅(SR)₁₈, 1.7 nm Au₁₃₃(SR)₅₂, 2.2 nm Au₂₄₆(SR)₈₀ and Au₂₇₉(SR)₈₄ nanoclusters (where, SR = thiolate). These perfect nanoparticles (i.e. uniform structures and no defects) serve as model systems for addressing many fundamental questions that were previously difficult or impossible to tackle, such as the origins of chirality, periodicities in nanoparticle growth, structural isomerism, metallic-to-nonmetallic transition, single-atom level doping, atomic-level details of self-assembly, and many other mysteries at the nanoscale. The attainment of atomically precise nanoparticles will offer exciting opportunities in future studies on functional materials.

Particle structural stability and mobility on the substrate critically affects their catalytic performances and aggregation propensity. Here, by using atomic resolution in-situ environmental transmission electron microscopy, we reveal size-dependent structure dynamics of single gold (Au) nanoparticles on ceria in CO oxidation environment at room temperature. While large Au nanoparticles remain rigid in the catalytic working condition, ultrasmall Au clusters lose their intrinsic structures and become disordered, featuring vigorous structural rearrangements and formation of dynamic low-coordinated atoms on surface. Ab initio molecular-dynamics simulations reveal that the interaction between ultrasmall Au cluster and CO molecules leads to the dynamic structural response, demonstrating that the shape of the catalytic particle in the relative environment may totally differ from the shape under the vacuum condition. The present observation provides insight on the origin of superior catalytic properties of ultrasmall gold clusters. In addition, we also demonstrate the substrate effect on the mobility of Au nanoparticles. Surface steps on ceria can pin the motion of Au clusters; while Au nanoparticles readily moves and aggregates on amorphous SiO_x substrate.

Particle-based crystallization (PBC) is a useful approach to build up nanomaterials with desired functionality by controlling the properties of metal nanoparticles as building elements. Atomically-precise gold nanoclusters have gained broad interest as the building unit for functional nanomaterials because of their unique quantum state and related intriguing properties. These nanoclusters exhibit non-metallic electronic structure unlike bulk or plasmonic nanoparticle of gold, and their electronic structure is very sensitive to the size and structure of nanoclusters, even to the atomic level of difference. Recent advances in controllable synthesis allow chemists to tailor the size/structure of nanoclusters with atomic precision, providing new opportunities to control the functionality at single atom level. Further improvement of the tailoring method is expected through the investigation of some fundamental questions regarding the quantum state of nanoclusters. For example, the question on the transition from non-metallic to metallic state still remains elusive due to the difficulty in atomically precise preparation of nanoclusters near the transition size region (i.e., ~2 nm). The answer to this central question has been eagerly pursued because the exploration near the critical size can give us further insights into the formation of metallic bond and the origin of surface plasmons. The critical factors to tailor the non-metallic properties also have been investigated toward the general rule on the unprecedented size dependence of the nanoclusters’ functionality.
In this presentation, I will discuss the successful identification of the transition from non-metallic to metallic state for Au nanoclusters at atomic level of precision, as well as the critical factors to atomically control the non-metallic properties below the transition regime. I will first talk about the synthesis and optical properties of atomically precise Au₂₇₉(SR)₈₄. Further characterization by ultrafast spectroscopy revealed metallic state of the Au₂₇₉ particle based on its laser power dependent dynamics, which is in contrast with the nonmetallic state of the previously reported Au₂₄₆(SR)₈₀. The abrupt transition with merely 33 metal atom difference is unprecedented, and it goes against >50 years of theoretical prediction of smooth transition.
I’ll also talk about atomic tailoring of Au nanoclusters to manipulate their non-metallic properties. I have synthesized Au₃₀(SR)₁₈ with an exotic crystalline phase: hexagonal close-packed (hcp) structure. The excited state dynamics of hcp-Au₃₀ is studied by ultrafast spectroscopy, and compared with other two nanoclusters with different crystalline phases: body-centered cubic (bcc) Au₃₈S₂(SR)₂₀ and face-centered cubic (fcc) Au₃₆(SR)₂₄. The observed lifetimes of hcp-Au₃₀ and bcc-Au₃₈ are 1 ns and 4.7 μs, respectively, demonstrating that controlling the crystalline phase of Au nanoclusters has significant effects on the excited state lifetime with three-orders-of-magnitude alteration.
The discovery of the non-metal to metal transition and the crystalline phase effect has provided critical insights into the quantum state of gold nanoclusters at atomic level. Further studies toward the direction will guide one to the strategy to engineer the functionality of nanomaterials by quantum state manipulation for applications in optoelectronic, catalysis, and biomedicine, as well as quantum computing.

Solution process is often used in the assembly and crystallization of molecular or ionic substance and clusters. We developed several strategies making use of the behaviors of the liquid fluids to control the assembly and crystallization. Both the temperature gradient and composition gradient were used to manipulate the Marangoni flow of the solution. By using a top-heating-bottom-cooling (THBC) setup, a steady Marangoni flow with a single vortex was created in the thin liquid film on solid substrates to facilitate the patterning of materials. By dropping dispersions of nanomaterials in water soluble organic solvents on the surface of water, Marangoni flow formed spontaneously and pushed the nanomaterials outside to form a thin film floating on water. We also studied the behavior of water-insoluble organic droplets on water surface. The three phase contact lines are tunable and thus the self-division process of the droplets was manipulated, which were further used to assemble materials. We show with the above examples that fluidics is a powerful tool in controlling the solution-based crystallization and assembly.

Composites consisting of carbon nanostructures, such as graphene and carbon nanotubes, and metals are desirable for power transmission lines, interconnects and heat transfer applications due to the combination of excellent charge carrier mobility, thermal conductivity and mechanical strength of the carbon nanostructures and the high density of electrons in the metal. There have been metal/nanocarbon composites made by different methods, such as, chemical vapor deposition, friction stir, ball milling, and plasma spraying that have produced materials with enhanced hardness and tensile strength. However, in many instances the electrical and thermal conductivities of the metal/nanocarbon composites deteriorate. In the case of aluminum and its alloys, for example, very frequently these fabrication methods give rise to the formation of Al₄C₃ which is the culprit in the worsening of the electrical and thermal properties of the metal. We are using electrocharging assisted process (EAP) to assemble graphene nanoribbons inside a liquid metal. EAP consists of the application of a high DC current to a mixture of liquid metal and carbon particles. The current in the EAP pulls out atoms from the carbon particles which assemble into C-C chains that eventually form ribbons. The ribbons become crystalline with the same structure as graphene nanoribbons forming a 3D network in the matrix of the metal. The EAP not only crystallizes the ribbons into graphene structures but the ribbons become nucleation sites for the metal during solidification. Raman scattering, TEM and XPS show that the carbon nanostructures have primarily sp2 bonding, they have a preferred orientation with the crystalline lattice of the metal and a nanocarbon crystallite size that increases with duration of the applied current. Al-C nanocomposites prepared with the EAP have shown 5 % increase in electrical conductivity as well as increase in the local stiffness, as measured by nanoindentation, compared to the pure Al alloys. Molecular dynamic simulation shows that graphene nanoribbons block the propagation of dislocations in the aluminum. Current AFM also indicates an increase in the local current from these samples compared to the parent aluminum alloy.
Funded by DOE EERE under Award No. EE0008313.

Engineering various types of structures through self-assembly of colloidal particles is a powerful approach in material design and processing. While simple colloidal building blocks, such as spherically symmetric particles, provide a number of well-known structures, more complex building blocks are needed to create novel structures with desired functionalities and tunable properties. Multicomponent building blocks such as colloidal molecules can provide a versatile platform for engineering new structures. However, in many cases, the synthesized colloidal molecules may end up suffering from ‘defects’ that are generally deemed to be an undesirable characteristic for multicomponent building blocks.

In this study, we use computational techniques to identify, investigate, and exploit self-assembly paradigms that are made possible through the use of defective colloidal molecules. Specifically, we study how defective units, which are typically missing one or two particles compared to the regular units, can be taken advantage of in order to build finite-size constructs that would otherwise be inaccessible. We further demonstrate different types of ordered superstructures that can be assembled through engineered directional interactions between defective and regular colloidal molecules. We use Molecular Dynamics (MD) and Brownian Dynamics (BD) simulations to study the thermodynamics and kinetics of self-assembly, and investigate the phase behavior of the resulting colloidal constructs as a function of building block size and shape. This study will generate an understanding of different possibilities for self-assembly of defective multi-component colloidal building blocks and provide guidelines for future experimental studies to target new material design approaches.

Anisotropic nanocrystals with defined surface patchiness represent a unique class of building objects for constructing high-order architectural nanomaterials. When utilizing in assembly, on the one hand, anisotropic nanocrystals can display strong asymmetric interactions induced by the patchiness that may complicate the formation of ordered structures compared to the assemblies of isotropic building blocks. The same asymmetric interactions, on the other hand, can not only result in novel translational orderings, but also induce correlations between the atomic orientations of HNCs upon crowding, thus possibly dictate and control the atomistic lattices within the assembled superstructure. In this talk, I will use several types of anisotropic 'patchy' nanocrystals as examples to demonstrate how they assemble into the unprecedented superstructures through the directional interactions among the building blocks under an enthalpy-driven condition. Both translational periodicities and orientational ordering of the final superstructural materials will be discussed. The dominating driving forces lead to the obtained architectures will be identified through molecular dynamics computer simulations and experimental results.

The increasing prevalence of drug resistance to the majority of existing antibiotics has generated a pressing global healthcare crisis. Certain highly resistant bacteria have acquired multiple mechanisms against all available antibiotics including the drugs of last resort. We are developing new strategies to combat antimicrobial resistance, for example, nanoantibiotics in the form of nanoaggregates or nanoclusters. In one study, we developed a modular synthesis of fluoroquinolone derivatives which are propeller-shaped. Upon precipitation into water, these compounds readily assembled into amorphous nanoaggregates that displayed enhanced luminescence. Furthermore, the nanoaggregates exhibited up to 2 orders of magnitude enhancement in the antibacterial activity. In the second example, our recent work on antimicrobial gold nanoclusters will be discussed. We have shown that the cluster structure has a profound impact on the antibacterial activity of the nanoclusters. Additionally, by modulating the ligand structure and composition, Gram-negative activity against Pseudomonas aeruginosa was enabled.

Bloodstains provide admissible information for crime scene investigators. The ability to resolve latent bloodstains that are commonly found in real scenarios is therefore pivotal to public security. Here, we report a facile approach for invisible bloodstain visualization based on the click reaction between serum albumin and tetraphenylethene maleimide (TPE-MI), an aggregationinduced emission luminogen (AIEgen). Compared to the widely adopted methods based on the harsh catalytic oxidation activity of hemoglobin, this working principle benefits from the specificity of the mild catalyst-free thiol−ene click reaction that improves the reliability and resolution. In addition, the mild conditions preserve DNA information and bloodstain patterns, and the excellent photophysical properties of the AIEgen afford high sensitivity and stability (>1 yr). Such an excellent performance cannot be achieved by conventional AIEgens and aggregation-caused quenching luminogens with similar structures. TPE-MI outperforms the benchmark luminol-based technique in visualizing latent bloodstains as showcased in two mock crime scenes: spattered blood track and transfer blood fingerprint. This disclosed method is an advancement in forensic science that could inspire future development of technology for bloodstain visualization.

Light emitting materials are nowadays important compounds in various applications and for many of them the developments of emissive organic molecules have opened new opportunities for future technologies.[1] However, even though organic materials show strong emission, their solution-processing remains challenging and morphology control as nanoparticles suffers from large distributions over size and shape.[2] A possible way to enhance the emission of organic fluorophores and to control the size of solution-processable emissive nanoparticles at the same time is their grafting onto inorganic nanoparticle surfaces. In order to avoid the classical aggregation-caused quenching (ACQ) effect [3] when high concentrations of organic ligands are present on nanoparticle surface, the opposite effect, namely aggregation-induced emission (AIE) [4] is a promising approach to generate strong light emission. Indeed, in this case, the high concentration helps to freeze the motion of the molecules to reduce the non-radiative deactivations. In this work, we thus present the synthesis of AIE nanohybrids prepared via the grafting of organic AIE ligands onto high band gap semiconducting nanoparticles. These organic-inorganic core-shell systems are composed of ZnO nanospheres as core and AIE ligands as shell. The design of the efficient AIE fluorophores is based here on hydroxy-oxophosphole luminophores, which can easily be grafted on metal oxide semiconductors. The structure-properties relationships leading to the highly emissive properties have been investigated. Thanks to theoretical calculations and XPS analyses, we could show that the electronic coupling between the ligands and the ZnO nanoparticles leads to partial charge transfer from the ligand to the ZnO core. Additionally, we showed that the grafting of these phosphole ligands onto ZnO nanoparticles introduces first a strong emission enhancement by the suppression of the hydroxyl resonator of the hydroxy-oxophosphole function that is electronically coupled to the emitting pi-system. Furthermore, the restriction of intra and inter molecular motions, through cluster formation (in solution) or highly emissive thin film processing, is found to introduce a second emission enhancement due to AIE effect. Preliminary tests in LED configuration using these AIE nanohybrids as emissive layer were obtained, that could demonstrate the potential of this new class of nanomaterials to be used as electroluminescent material by taking the advantage of combining both the AIE effect and the transport properties of the inorganic scaffold.

[1] N. Thejo Kalyani Hendrik Swart S. J. Dhoble. 2017 Woodhead Publishing. ISBN: 9780081012130
[2] Ying Diao, Leo Shaw, Zhenan Bao, Stefan C. B. Mannsfeld. Energy & Environmental Science, 2014, 7, 2145.
[3] a) Park, S.-Y.; Kubota, Y.; Funabiki, K.; Shiro, M.; Matsui, M. Tetrahedron Letters 2009, 50, 1131. b) Park, S.-Y.; Ebihara, M.; Kubota, Y.; Funabiki, K.; Matsui, M. Dyes and Pigments 2009, 82, 258. c) Ooyama, Y.; Okamoto, T.; Yamaguchi, T.; Suzuki, T.; Hayashi, A.; Yoshida, K. Chem. Eur. J. 2006, 12, 7827. d) Shirai, K.; Matsuoka, M.; Fukunishi, K. Dyes and Pigments 1999, 42, 95.
[4] Y. Hong, Y. ; Lam, J. W. Y. ; Tang B. Z. Chem. Commun. 2009, 4332.

In nature, protein subunits on the capsids of many icosahedral viruses form rotational patterns, and mathematicians also incorporate asymmetric patterns into faces of polyhedra. By taking inspiration from nature and mathematics, we used pseudo-chiral truxene (Tr) and triazotruxene (TAT) derivatives as building blocks to construct a series of molecular polyhedra with rotational patterns on faces, which we term as Face-Rotating Polyhedra (FRP). FRP represent a special form of molecular chirality. The relative stability of these polyhedra enables separation by chiral HPLC and full characterization. We also investigated the assembly process and the kinetics of interconversion of the polyhedra by a combination of chiral HPLC, CD, MS and NMR.
Tetraphenylethylene (TPE) and its derivatives, as well-known AIE chromophores, have been extensively studied due to their broad applications in many fields. TPE unit exhibits either M or P configuration in its propeller structure when the free rotation of phenyl rings was hindered, making it a possible building block for FRP. We assembled TPE units with triamine to construct cubes or sandwich-like assemblies with “emergent” chirality and fluorescence. This study provides strategies to construct FRP by means of AIEgens, which can be applied in luminescent materials, chiral molecular recognition or asymmetric catalysis.
Reference：
Wang, X.-C.; Wang, Y.; Yang, H.-Y.; Fang, H.-X.; Chen, R.-X.; Sun, Y.-B.; Zheng, N.-F.; Tan, K.; Lu, X.; Tian, Z.-Q.; Cao, X.-Y.* Nat. Commun., 2016, 7, 12469.
Wang, Y.; Fang, H.-X.; Ionut, T.; Qu, H.; Wang, X.-C.; Markvoort, A. J.*; Tian, Z.-Q.; Cao, X.-Y.* Nat. Commun., 2018, 9, 488.
Zhang, P.; Wang, X. -C; Xuan, W.; Peng, P.-X.; Li, Z.-H.; Lu, R.-Q; Wu, S.; Tian, Z.-Q.; Cao, X.-Y.* Chem. Commun., 2018, 54, 4685
Mei, J.; Leung, N. -L.; Kwok, R. -T.; Lam, J. -W.; Tang, B.-Z. * Chem. Rev., 2015, 115, 11718
Qu, H.; Wang, Y. *; Li, Z.-H.; Wang, X.-C.; Fang, H.-X.; Tian, Z.-Q.; Cao, X.-Y.* J. Am. Chem. Soc., 2017, 139, 18142.
Qu, H.; Tang, X.; Wang, X.-C.; Li, Z.-H.; Huang, Z.-Y; Zhang, H.; Tian, Z.-Q.; Cao, X.-Y.* Chem. Sci., 2018, 9, 8814

Through the A₄ + B₂ type Suzuki-Miyaura coupling reaction, hyperbranched polymers CP1, CP2, and CP3 were easily prepared, which exhibited high luminous efficiency in solution, neat film, and solid state as well as good thermal stability. When fabricated into organic light-emitting diodes (OLEDs) with mCP as host, the device based on CP1 demonstrated the good EL performance with external quantum efficiency (EQE) up to 6.36%. While the bipolar TADF host of CzAcSF was utilized instead of mCP, the driving voltage (at luminescence of 10 cd m-2) decreased from 5.7 to 4.4 V, and the EQE further increased to 9.74%, which was the highest EQE reported for hyperbranched polymers.

Crystalline morphologies exist in many synthetic and natural macromolecules and are believed to play an essential role in biological phenomena and materials science. Despite the high performance of fluorescence imaging in spatial morphology characterization in life science, high-contrast mapping across different microstructures in solid polymers is challenging. In thiswork, we demonstrated a strategy to impart aggregation-induced emission (AIE) and polymorphic characteristics in a single luminescent system, whose polymorphic crystalline states with distinct emission are generated selectively in amorphous and crystalline phases of a polymer to light up the whole morphology. High compatibility between the AIEgen and polymer matrix allows the sensitivity of the AIEgen to be visually shown as different emissions. Consequently, information of the polymer morphology (crystalline and amorphous phases) is transformed into distinct fluorescence colors, allowing a single AIE molecule as a fluorescent marker for multiscale visualization of polymer morphologies in terms of amorphous and crystalline phases distribution, quantitative polymer crystallinity measurement, and spatial morphological arrangement. The proposed strategy provides a correlation between microscopic morphologies and macroscopic optical signals, opens an avenue of fluorescence imaging in materials science.

The development of rational design principles for electronic materials is crucial to ensure efficient device performance and favorable optical properties. Small molecule phosphors are becoming increasingly important for OLEDs, optical sensing, and display technology. Heavy transition metals such as palladium and platinum enhance spin-orbit coupling of chromophores by mixing the energy levels of the singlet and triplet states, allowing for faster intersystem crossing and a population of excited triplet states. Solid-state phosphorescence, however, is susceptible to aggregation-caused quenching (ACQ) through non-radiative processes, which significantly diminish phosphorescent quantum yield of neat solids. Herein, we present progress on an approach to ameliorate this problem by utilizing structural components of the molecules themselves to suppress chromophore aggregation and prevent ACQ. Specifically, we demonstrate aggregation induced enhancement of phosphorescence using a series of ester substituted phosphorescent platinum acetylides. Perfluorinated arene pendant groups on these chromophores encourage coplanar aromatic stacking interactions between adjacent molecules, insulating excited chromophores from non-radiative quenching typically associated with aggregation of phosphors. Fluorinated compounds show strong solid-state phosphorescence, which we attribute to fluoroarene-arene stacking interactions that prevent inter-chromophore aggregation, as demonstrated through their X-ray crystal structures. In contrast, non-fluorinated compounds show very little solid-state phosphorescence, a consequence of cofacial chromophore aggregation. This work highlights the potential broad utility of the non-covalent stacking interactions of fluorinated arenes in the development of solid state phosphors.

Mesocrystals formed from assembled nanoparticles with ordered alignment have attracted much attention as promising materials in various engineering fields, such as photocatalysis, energy storage, and optical/magnetic application including metamaterials.
Hydrothemal method with flow-type reactor can produce not only nanoparticles, but also mesocrystals, continuously [1]. However, the mesocrystal structure/size is difficult to control because the structural formation mechanism of the secondary structure of nanoparticles has not been clarified. In this study, to investigate the mesocrystal formation process, we conducted time-resolved experiments in the order of seconds using flow-type hydrothermal reactor [2].
We employed L-glutamic-acid-modified CeO₂ nanoparticle as the building block of mesocrystal. The cerium nitrate solution with L-glutamic acid was pumped into the flow-type reactor, continuously, and mixed with preheated water at a T-shaped mixer. The temperature and pressure in the reactor tube was maintained at 548 K and 25 MPa. The reaction time was varied by altering the length of the reactor tube. In the hydrothermal reactor, the precursor reacts to form the L-glutamic-acid-modified CeO₂ nanoparticles and the produced nanoparticles assembles by the L-glutamic acid as a glue to form mesocrystals.
The snapshots of the produced materials during formation process of mesocrystal were obtained by HRTEM and XRD observations for the clusters synthesized from 0.7 s to 8.0 s. Here, we found that the primary nanoparticles in the loose agglomeration order themselves to form a cubic CeO₂ mesocrystal. At a reaction time of 0.7 s, the truncated octahedral CeO₂ nanoparticles (ca. 20 nm) aggregated in spherical shape (ca. 72 nm) with polycrystal structure. However, the structure of the cluster changed from spherical to cubic in less than 8.0s. The diffraction pattern of the cubic clusters gives a crystalline structure resembling that of a single crystal by rearrangement of the primary building blocks.
These formation dynamics can be regarded as the analogy to the conventional crystalline particle formation. In the case of crystalline particle formation, nucleation occurs from monomers via non-crystalline droplet, followed by crystal growth with monomer diffusion to the crystal surface. In the case of the mesocrystal formation in this system, non-ordered agglomeration of primary nanoparticles firstly formed, followed by orientation of primary nanoparticles and mesocrystal growth with primary particle attachment. Consequently, the agglomeration of nanoparticles can be regarded as nucleation, and the orientation and growth can be regarded as the crystal growth, which can be seen in the conventional crystalline particle formation.
Based on the idea that nanoparticles behave like monomers in conventional particle formation, we conducted size control of mesocrystal. In conventional particle formation, the nanoparticle concentration and the solvent properties affects the nucleation and crystal growth, determining particle size. For example, using the same flow-type hydrothermal reactor, the unmodified CeO₂ nanoparticles became smaller with lower precursor concentrations and the addition of ethanol as antisolvent. On the other hand, in the case of mesocrystal formation from L-glutamic-acid-modified CeO₂ nanoparticles, the mesocrystal size also decreased with the decrease in the precursor concentration and with addition of the ethanol, antisolvent.
[1] A. A. Litwinowicz, S. Takami, D. Hojo, N. Aoki and T. Adschiri, Chem. Lett., 2014, 43 , 1343 -1345.
[2] A. A. Litwinowicz, S. Takami, S. Asahina, X. Hao, A. Yoko, G. Seong, T. Tomai and T. Adschiri , CrystEngComm, 2019, in press.

PbSe honeycomb superstructures, recently obtained by the self-assembly of PbSe nanocrystals (NCs) at fluid-fluid interfaces [1], have attracted a great interest since their predicted optoelectronic properties should combine the virtues of graphene with those of semiconductors [2]. However, their formation mechanism is still far from understood [3].

With a new coarse-grained molecular dynamics model we are able to reproduce the self-assembly of PbSe NCs in honeycomb and other observed 2D superstructures [4]. Our results shed light on the superstructure formation dynamics by identifying and quantifying the key parameters that drive the NC self-assembly into one or another superstructure. In particular, we show how the obtained NC superstructure depends on an intricate interplay between the interface-adsorption forces experienced by the NCs at the fluid-fluid interface and short-range electrostatic forces between the NCs. We also show indications that our model can be applied to study the formation and stability of defects in the self-assembled superstructures.

[1] M. P. Boneschanscher, W. H. Evers, J. J. Geuchies, T. Altantzis, B. Goris, F. T. Rabouw, S. A. P. van Rossum, H. S. J. van der Zant, L. D. A. Siebbeles, G. van Tendeloo, I. Swart, J. Hilhorst, A. V. Petukhov, S. Bals, and D. Vanmaekelbergh, Science 344, 1377 (2014).
[2] E. Kalesaki, C. Delerue, C. Morais Smith, W. Beugeling, G. Allan, and D. Vanmaekelbergh, Physical Review X 4, 011010 (2014).
[3] K. Whitham, D Smilgies, and T.Hanrath, Chemistry of Materials 30, 54 (2018).
[4] G. Soligno and D. Vanmaekelbergh, Physical Review X 9, 021015 (2019).

PbSe nanocrystals have attracted considerable attention because of their potential applications in solar cells, light emitting diodes and field effect transistors. Monodisperse nanocrystals form superlattices with emergent collective properties. Although there have been intensive studies on PbSenanocrystal superlattices, how individual nanocrystals change and how they interact with each other during superlattice transformations are largely unknown. Direct observation with high spatial and temporal resolution using transmission electron microscopy (TEM) provides the opportunity to address these questions.We developed high-resolution carbon-film liquid cells, which allow to directly observe PbSe nanocrystal superlattice transitions using TEM. A monolayer of hexagonal superlattice of oleate-capped PbSenanocrystals is used as the starting materials. During its transformation into a square lattice due to ligand displacement, we observed an unexpected phenomenon that PbSe semiconductor nanocrystals can drastically change shape depending on the chemical environment. For example, ethylenediamine (EDA) induced oleate removal increases the nanocrystal dipole-dipole interactions, triggering the large shape changes and rapid nanocrystal fusion. After the ligands are removed, PbSe nanocrystals experience drastic directional shape deformation when the spacing between two nanocrystals reaches 2–4 nm. Moreover, the deformation can be completely recovered when two nanocrystals move apart or it can be retained when they attach. We have also performed the superlattice phase transition in pure ethylene glycol (EG) and found nanocrystals maintain their original shape during self-assembly, the resulting superlattices are more uniform and less defective. The large deformation, which is responsible for the structural defects in the epitaxially-fused nanocrystal superlattice, likely arises from inter-nanocrystal dipole–dipole interactions. This has been further testified by our molecular dynamics (MD) simulations.

References:
[1] X. Peng, A. Abelson, Y. Wang et al., “In situ TEM study of the degradation of PbSe nanocrystals in air.” Chemistry of Materials 31, 190-199 (2019).
[2] Y. Wang, X. Peng, A. Abelson, et al.,“Dynamic deformability of individual PbSe nanocrystals during superlattice phase transitions.” Science Advances 5, eaaw5623(2019).
[3] Y. Wang, X. Peng, A. Abelson, et al.,“In situ TEM observation of neck formation during oriented attachment of PbSe nanocrystals.” submitted (2019).

Layer-by-layer growth has been a hallmark of atomic crystallization to produce flat films of semiconductors or alloys for device applications, where a new surface layer starts to develop only after the preceding layer is complete. Here we show the direct imaging of nanoparticles crystallizing in a layer-by-layer fashion to large-scale superlattices with flat surfaces, utilizing the protocols we have developed in low-dose liquid-phase transmission electron microscopy (TEM). Single-particle tracking of the real-space, real-time TEM movies not only elucidates the structure and surface morphology of the superlattice during growth, but also enables the measurement of key parameters associated with layer-by-layer growth that are otherwise inaccessible. Coupling the in-situ observation with molecular dynamics simulation, we reveal the energetic origin of the layer-by-layer growth in our system by mapping the free energy landscape. Changing the pairwise interparticle interaction leads to other atomic crystallization pathways to occur in the same system, including roughening transition and coalescence. These atom-mimicking crystal growth pathways have hardly been realized in micron-sized colloids, suggesting a fundamental importance of the length and time scale associated with nano-sized building blocks.

Controlled and predictable growth through oriented attachment (OA) mechanism is still a challenge. Here, we describe a simple approach to control the OA process through selective ligand scavenging from the {100} facets of CeO₂ nanoclusters. Aggregates of these nanoclusters smaller than 10 nm with controlled cuboid shape were obtained. For the synthesis of the cuboctahedral CeO₂ nanoclusters, we developed a solvent-controlled synthesis approach based on a nonhydrolytic sol-gel process and used an ester aminolysis reaction to control ligand scavenging from the {100} facets. First-principle calculations allowed us to understand and interpret, at the molecular level, the effects of shape control on the growth process. Fine-tuning of the desired morphologies can be achieved by controlling the values of the surface energies, which leads to the formation of morphologies that the classic growth process does not allow. The methodology described in this work, for the controlled assembly of CeO₂ nanoclusters, may be relevant for the investigation of self-assembly processes of other metal oxides as well as for other types of inorganic nanoparticles in future work, which means that it brings new insight for nanostructure design and controlled synthesis.

Total synthesis, where desired organic- and/or bio-molecules could be produced from simple precursors at atomic precision and with known step-by-step reactions, has prompted centuries-lasting bloom of organic chemistry since its conceptualization in 1828 (Wöhler synthesis of urea). Such expressive science is also highly desirable in nanoscience, since it represents a decisive step towards atom-by-atom customization of nanomaterials for basic and applied research. Although total synthesis chemistry is less established in nanoscience, recent years have witnessed seminal advances and increasing research efforts devoted into this field. In this talk, I will discuss our recent work on introducing and developing total synthesis routes and mechanisms for atomically precise metal nanoclusters (NCs). Due to their molecular like formula and properties (e.g., HOMO-LUMO transition, strong luminescence and stereochemical activity), atomically precise metal NCs could be regarded as “molecular metals” (or metallic molecules / molecular-like metals), holding potential applications in various practical sectors such as biomedicine, energy, catalysis and many others. More importantly, the molecular-like properties of metal NCs are sensitively dictated by their size and composition, suggesting total synthesis of them as an indispensable basis for reliably realizing their practical applications.

The aggregation-induced emission (AIE) phenomenon was first reported by Tang and coworkers in 2001 and this new phenomena has been utilized to revolutionize biological and optoelectronic materials for use in various scientific fields over the past two decades. Due to the importance of AIE, thousands of publications have been reported on developing new efficient AIE luminogens (AIEgens) and implementing them for practical applications. Although conical intersection, E/Z isomerization, proton transfer, charge transfer, intra- and inter molecular restrictions have been considered as the main reasons for the phenomenon of AIE to occur in a number of different systems, there have been few direct pieces of evidence reported to support these hypotheses.
The time-resolved spectroscopy techniques are considered to be powerful tools for studying and characterizing the mechanisms of AIE materials. Here, we report the use of transient absorption and time-resolved resonance Raman to study a number of TPE-based derivatives with varying structural rigidity and AIE properties. This allowed an examination of the direct correlation between the state-dependent coupling motions and inhibited fluorescence. Our new results prove the existence of photocyclized intermediates in several systems. We demonstrate that the dominant non-radiative relaxation dynamics i.e. formation of an intermediate or rotation around the elongated C=C bond, is responsible for the AIE effect, which is strongly structure-dependent but not related to structural rigidity. In addition, femtosecond transient absorption spectroscopy was also employed to demonstrate that the excited state aromaticity inversion for the non-aromatic annulene derivative of cyclooctatetraene causes the typical AIE phenomenon for this system in spite of its rotor-free structure. Therefore, results from the study of the photophysical and photochemical mechanisms of AIEgens will be instructive to guide the tailoring and further development of more efficient luminogens in the future.

Small, apolar aromatic groups, such as phenyl rings, are commonly included in the structures of fluorophores to impart hindered intramolecular rotations, leading to desirable solid-state luminescence properties. However, they are not normally considered to take part in through-space interactions that influence the fluorescent output. This presentation will detail (Figure 1) the photoluminescence properties of a series of phenyl-ring molecular rotors bearing three, five, six, and seven phenyl groups around carbacyclic cores. The fluorescent emissions from some of the rotors are found to originate, not from the localized excited state as one might expect, but from unanticipated through-space aromatic-dimer states.^[1] We demonstrate that these relaxed dimer states can form as a result of intra- or intermolecular interactions across a range of environments in solution and solid samples, including conditions that promote aggregation-induced emission. Computational modeling also suggests that the formation of aromatic-dimer excited states may account for the photophysical properties of a previously reported luminogen. These results imply, therefore, that this is a general phenomenon that should be taken into account when designing and interpreting the fluorescent outputs of luminescent probes and optoelectronic devices based on fluorescent molecular rotors. In order to gain deeper insights, we have also taken a ‘minimum modification’ strategy to modify the conjugation and geometries present for one of the rotors, sym-heptaphenylcycloheptatriene.^[2]

References
[1] J. Sturala, M. K. Etherington, A. N. Bismillah, H. F. Higginbotham, W. Trewby, J. A. Aguilar, E. H. C. Bromley, A. J. Avestro, A. P. Monkman, P. R. McGonigal, J. Am. Chem. Soc. 2017, 139, 17882.
[2] A. T. Turley, A. N. Bismillah, A. Mallick, M. K. Etherington, A. P. Monkman, D. S. Yufit, B. Curchod, P. R. McGonigal, manuscript in preparation.

The abnormality of plasma membrane (PM) is an important biomarker for cell status and many diseases. Therefore, visualizing PM is crucially important in the fields of physiology, pathology and pharmacology^1-2. Herein, we provide an effective way to generate dyes that suitable for PM imaging with easy operation (one step), rapid staining, good biocompatibility and high-fidelity imaging. Four compounds with aggregation-induced emission (AIE) characteristics were presented by changing the length of alkane chain and electrostatic interaction to investigate the relationship between amphipathy and positive charges as well as the imaging effect including specificity, staining period and dyeing continuity and retention. Besides, the 2D/3D imaging experiments indicated the high specificity of PM and ultrafast imaging without washing (2D at the second-level, 3D around 1 hour). More importantly, the probe Pent-TMP could light up the PM in complex systems (brain tissue and live zebrafish). For the first time, we have captured single erythrocyte in brain tissue by fluorescence. Besides, Pent-TMP could stain the PM of the zebrafish in vivo which typical probes can hardly do³. With these advantages, we hope that this method of constructing ultrafast and easy-operation PM Specific Probes will be helpful to molecular design, medicine and biology.

Efficient pure organic room temperature phosphorescence (RTP) materials have drawn considerable attention. So far, most pure organic RTP molecules are aromatic compounds, and nonconjugated molecules are really scarce. The only few reported non-aromatic organic phosphorescence materials are polymers without confirmed subtle structures, and there are no reports concerning non-aromatic organic small molecules with persistent RTP. Here, we report an example of a pure non-aromatic organic small molecule, cyanoacetic acid, that shows unexpected persistent RTP behavior with RTP lifetime as long as 862 ms. According to the CAA crystal and theoretical calculations, the presence of strong intermolecular hydrogen bonds is the key factor for its persistent RTP effect. This discovery demonstrates a clear relationship between the molecular structure, packing mode and RTP effect in the non-aromatic system, which will largely extend the current pure organic RTP systems to deeply investigate the origin of light emission

Bimetallic nanoparticles are commonly used as catalysts in a broad range of industrially relevant reactions. To enable the rational design of catalysts with better performance, it is necessary that we understand the relationship between a nanoparticle’s structure and its catalytic properties. However, such insights have to be obtained from catalysts under reaction conditions because the nanoparticles can exhibit dynamical structures that do not exist outside the reactive environment. TEM has always been a powerful technique for studying the detailed structure of nanoparticles. Recent developments in in situ environmental TEM, now allow us to study nanostructures within gas and liquid environments with TEM, and probe their formation pathways during the synthesis and reaction kinetics during the catalysis in real-time with nanometer resolution.
In the first part of my talk, using in situ liquid phase TEM, I will describe how bimetallic nanoparticles with different architectures form in solution. By directly visualizing the growth and electrochemical etching of such nanoparticles, I will show how bimetallic nanoparticles form under different physical and chemical environments.
Next, using in situ gas phase TEM imaging, I will discuss the catalytic performance of these bimetallic nanoparticles and describe how these nanoparticles exhibit surprising structural changes during catalytic reactions. Using Pt-Ni bimetallic nanoparticles as a model system, I will show that these nanoparticles evolve differently in reactive gas conditions depending on the starting structure of the nanoparticle.
These insights into the evolution of nanoparticles both during their synthesis and application are important for the rational design of nanomaterials with tailored properties.

Materials that combine synthetic and biological nanotechnologies are inspired by Nature’s tight control over organic-inorganic interactions, such as in biomineralization, to assemble biological nanomaterial hybrids with optimized performance. Although engineering synthetic-biological hybrids would accelerate the development of next-generation materials, there are currently no design rules to effectively create these synthetic/biomimetic systems. This is largely due to a gap in knowledge of the interface between biological-synthetic materials and the fundamental interactions that govern their formation. Here, we establish an initial understanding of the interactions between bovine serum albumin (BSA) protein and metal-organic framework ZIF8 using electron microscopy and reveal complex growth mechanisms that govern the final BSA/ZIF8 single-crystal nanomaterial. By varying the amount of BSA incorporated into an in-situ ZIF8 synthesis, we observe significant control in the final crystal size, morphology, and porosity ranging from well-faceted dense crystals to porous crystals with rough surfaces. Using time-resolved cryotransmission electron microscopy, we found that these structural differences stem from the simultaneous formation of two amorphous metastable phases and their dynamic interactions in the early stages of BSA/ZIF8 formation. One phase is characterized by well-defined primary particles (~ 8 nm) and the second phase is characterized by BSA/ZIF8-precursor clusters that aggregate into branched networks (~ 1 µm). Lattice-resolution cryoTEM demonstrates an important interplay between these two phases during crystallization and growth through particle aggregation mechanisms. Real-time observation of the transition between these phases is further probed with in-situ liquid TEM. The presence of these amorphous phases and their dynamic interactions to form the final BSA/ZIF8 crystals provides an understanding of protein-MOF crystal formation that is analogous with established biomineralization mechanisms.

One-dimensional polymer nanowires with highly ordered structure have fast carrier transport which is beneficial for improving polymer thermoelectric (TE) power factors. Tuning the nanowire structure and interfaces in conjugated polymer nanowires may lead to unique density of states and thus thermoelectric transports. In this talk, I will review our recent works that involve the structure and interface manipulation of conjugated polymer nanowires for higher thermoelectric performance, the possible TE enhancement mechanisms will be discussed as well.

With the development of semiconductor technology, the 10 nm feature size of fabrication is already achieved. It is thus quite essential to explore more precise nanofabrication and characterization method to evaluate the shape/structure stability and possible new properties of sub-10nm material components, especially under external stimuli such as strain, electric, or thermal fields. Along with the reduction of dimensions, the surface-to-volume ratio of the materials increases. For a 10 um particle, only about 0.036% of atoms occupy the surface positions, and the percentage rise to ~36% and ~62% for a 10 nm and a 6 nm particle respectively. Furthermore, surface atoms are preferably reconstructed for adapting their geometrical and electronic structure to the environment. Thus, the surface structure begins to dominate material properties ranging from electronic and structural aspects when the characteristic dimension is reduced to sub-10 nm. Here we review our recent progress in atomic resolution nanofabrication and dynamic characterization of sub-10nm individual nanostructures and nanodevices based on the idea of "setting up a nanolab inside a transmission electron microscope".

AIEgens including silole and tetraphenylethylene show abnormal emissive behavior. They are almost non-emissive in the well-dispersed states, but their emissions are switched on upon aggregation. By taking advantage of this unusual emissive property, AIE gens have been successfully employed for chemo-/biosensing, fluorescence imaging and photodynamic therapy. In this presentation, I will show that the emission colors and efficiencies of AIEgens are affected the aggregation of AIEgens in terms of intermolecular interactions and orientations. Moreover, I will discuss the dependence of cytotoxicity on the size and surface zeta potential of aggregates of AIEgens.
References
[1] Ming Wang, Xinggui Gu, Deqing Zhang, Guanxin Zhang, Daoben Zhu, Anal. Chem., 81 (2009) 4444.
[2] Fang Hu, Yanyan Huang, Guanxin Zhang, Rui Zhao, Hua Yang, Deqing Zhang, Anal. Chem. 86 (2014) 7987.
[3] Yanyan Huang, Fang Hu, Rui Zhao, Guanxin Zhang, Hua Yang, Deqing Zhang, Chem. Eur. J., 20 (2014) 158.
[4] Yanyan Huang, Guanxin Zhang, Fang Hu, Yulong Jin, Rui Zhao, Deqing Zhang, Chem. Sci., 7 (2016) 7013.

AIE has come a long way since its discovery almost 20 years ago. However, some questions about the basic mechanisms still remain open, and theory and computations can be very helpful in providing new fundamental insights. In this contribution we will center on how work from our group has contributed to a better understanding of the fundamental processes at the molecular level, both in solution and in the aggregate phase. We will center on two subjects: first, introduce our Restricted Access to a Conical Intersection (RACI) model to explain the photophysics/photochemistry in solution and in the crystal and discuss some examples (see for a review: Crespo-Otero et al, Chem. Asian J. 2019, 14, 700); and second, discuss some of the factors that affect morphochromism and, more in general, the emission color of AIEgens and their dependence on the aggregate form.

Mechanoluminescence (ML) is alight-emitting process induced by mechanical stimuli, such as grinding, rubbing, or shaking, which has attracted extensive attention because of its potential in displays,lighting, bioimaging,and stress-sensing applications. Regardless of its long history , which stems from the first report on sugar by Francis Bacon in 1605, reports on organic ML luminogens remain limited in number, partially because of alack of reliable guidance and unclear inherent mechanisms.Onthe other hand, as the most investigated light-emitting process,photoluminescence (PL) is well-understood and has made great contributions to research involving other kinds of emitting processes,including electroluminescence (EL) and chemiluminescence (CL). Based on these success stories ,and the previous reported ML luminogens ,wedecided to explore the unknown ML excitation process using wellunderstood PL as atemplate.

Micro-patterning of various materials was recently developed based on the laser-induced microbubble technique (LIMBT). LIMBT relies on the formation of a microbubble due to laser heating of a dispersion of nanoparticles (NPs) that absorb the laser light. Natural and Marangoni convection currents carry the NPs to the bubble/substrate interface where some of them are pinned. Moving the substrate relative to the laser beam results in deposition of NPs along a predetermined path. Unfortunately, for many materials this deposition is non-continuous.
We have found^[1] that controlling the construction and destruction of the microbubble through modulation of the laser enables the formation of continuous patterns by preventing the microbubble from getting pinned to the deposited material. Furthermore, we show^[2] that microstructure formation from an ion solution could be explained by a similar mechanism. Photo-thermal reduction of the metallic ions lead to formation of crystalline NPs. The NPs are then pinned to the bubble/substrate interface. These deposits absorb laser light, resulting in extensive local heating, which leads to fast thermal reduction of metal ions that are added as amorphous metal or metal oxides. The resulting deposition is therefore a combination of both crystalline and amorphous structures. This innovative approach could be applicable for producing thin conductive patterns and allow fabrication of microelectronic devices and sensors.

References
[1] N. Armon, E. Greenberg, M. Layani, Y. S. Rosen, S. Magdassi, H. Shpaisman, ACS Appl. Mater. Interfaces 2017, 9, 44214.
[2] E. Greenberg, N. Armon, O. Kapon, M. Ben-Ishai, H. Shpaisman, Adv. Mater. Interfaces 2019, 1900541.

Highly conductive molecular wires are an important component for realizing molecular electronic devices and have to be explored in terms of interactions between molecules and electrodes in their molecular junctions. Here, we report new molecular wire junctions (e.g., Co(II)(tpyphS)₂–AuNP–Co(II)(tpyphS)₂) to enhance charge transport through gold nanoparticle (AuNP)-linked double self-assembled monolayers (SAMs) of cobalt (II) bis-terpyridine molecules (e.g., Co(II)(tpyphS)₂). Electrical characteristics of the double-SAM devices are explored in terms of the existence of AuNP. The AuNP linker in the Co(II)(tpyphS)₂–AuNP–Co(II)(tpyphS)₂ junction acts as an electronic contact that is transparent to electrons. The weak temperature dependency of the AuNP-linked molecular junctions strongly indicates sequential tunneling conduction through the highest occupied molecular orbitals (HOMOs) of Co(II)(tpyphS)₂ molecules. The electrochemical characteristics of the AuNP–Co(II)(tpyphS)₂ SAMs reveal the fast electron transfer through molecules linked by AuNP. Density functional theory (DFT) calculations reveal that the molecular HOMO levels are dominantly affected by the formation of junctions. The intermolecular charge transport, controlled by the AuNP linker, can provide a rational design for molecular connection that achieves a reliable electrical connectivity of molecular electronic components for construction of molecular electronic circuits.

Molecular patterning of nanoparticles can allow prescribing inter-particle binding sites, and that can permit creating tailored building blocks for assembly of targeted nanoparticle clusters and large-scale periodic nano-organizations. However, establishing a platform for rational pattering of nanoparticles has been challenging. We have developed a so-called Molecular Stamping approach for 3D nanoparticle patterning by templating target particles with designed molecular patches using DNA frame. In this method, molecular stamps, located at the prescribed locations of frame, can be engaged for transferring distinctive molecules onto different sites of nanoparticle surface. Our approach allows for creating molecular patches with a single molecule control and with same or different binding affinities. We applied the developed method to generate planar and 3D arrangements of molecular patches on nanoparticles, and investigated factors affecting pattern formation and its resolution. The developed approach was used to create nanocluster architectures containing nanoparticles of different sizes and from different materials. Electron microcopy and tomography were utilized to reveal spatial arrangements of molecular patches and the factors contributing to the patterning process.

Colloidal nanoparticles have become essential components to a broad spectrum of scientific fields, accredited to their superior and tunable physicochemical properties exclusive to the nanoscale dimensions. For example, their exceptional surface to volume ratio, diffusion rate and dispersion stability markedly increase their reactivity and bioavailability. In addition, the colloidal nanoparticles exhibit diverse electromagnetic responses whose modes, intensities and spectral locations are readily adjusted according to the engineering needs. As such, colloidal nanoparticles have become integral optical-actuating platforms in catalytic reactions, targeted drug delivery, in vivo medical imaging and sensing. On the other hand, their ultraviolet and visible spectrum requirement for photo-stimulation poses intrinsic limitations due to poor light penetration into the reaction media and the biological tissues. Delivering optical energy through the ambient media within its specific transparency window that could trigger the target responses may immensely broaden the scope of the operation while enhancing its procedural compatibilities and efficiencies. Hence, robust in situ colloidal optical nonlinear transducer capable of all wavelength accessibility with practical conversion efficiencies could provide important solutions to these challenges.
Here, we demonstrate a versatile pathway to obtain second harmonic generation (SHG) of light with practial conversion efficiencies from dielectric ψ⁽²⁾ nanostructures by configuring them into a colloidal superparticle. Through one-pot chemical synthesis, we were able to blend multiple materials types of different constitutive properties, shapes and dimensions into a single colloidal superstructure in a hierarchical manner. An array ZnO nano-rods, a ψ⁽²⁾ material, are vertically aligned to construct a corrugated shell around a dielectric SiO₂ sphere. Extensive control over the chemical synthesis of the ZnO nanostructures enabled us to transform the nano-topographic landscape into a shell of optical metamaterials having 2^nd order nonlinearity (ψ⁽²⁾ meta-shell). Our analysis show that the ψ⁽²⁾ meta-shell exhibits radial graded index and anisotropy profile in its constitutive properties. The effective optical responses from the ψ⁽²⁾ meta-shell is engineered in the linear regime to maximize the optical nonlinear effects in the ψ⁽²⁾ meta-shell, the site of nonlinear conversion.
We have experimentally observed strong enhancement of SHG in the meta-shell superparticle. The FDTD simulation revealed 10⁴ enhancement in the conversion efficiency between the meta-shell superparticle and a ZnO nano-rod. Furthermore, the SHG generated by the meta-shell particle is highly localized within the nanoscale confines, making it a desirable platform for photo-chemistry, photo-medicine, biotechnology and bio-photonics. While the current demonstration focuses on the second harmonic generation, our colloidal meta-shell superstructure has the ingredients necessary for a cohort of optical nonlinear conversion processes.

3D chemically bonded nanostructures combine the unique properties of nanomaterials with the periodicity of interconnected structures and the form of bulk materials, giving rise to new physical phenomena. We have combined the strength of particle assembly and High Pressure confined Chemical Vapor Deposition¹ (HPcCVD) to create ordered and electrically continuous 3D nanostructures of both metals and semiconductors. These structures called “metalattices”(ML)² were made possible by void-free infiltration of silica colloidal crystals using HPcCVD. We use a vertical deposition technique³ to assemble monodisperse silica nanoparticles in the range of 14nm-120nm, at controlled temperature and humidity, to form 3D colloidal crystals. The arrangement of silica nanoparticles in the template has a direct effect on metalattice (ML) properties. Structural characterization of the colloidal crystal templates which were grown as micron-thick films on silicon substrates and of MLs using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) and Small Angle Xray Scattering (SAXS) shows a 3D-ordered and well connected structure. Extending this structural characterization of templates to metalattices, we are studying surface modification and spatial band gap modulation in Germanium metalattices. Germanium despite its high carrier mobility has suffered inefficiency in electronic applications due to formation of germanium oxide which is unstable and introduces defects at the interface. We use a core-shell approach to passivate Ge MLs and prevent oxide formation. A silicon shell is grown on the Ge core leading to the formation of a Si_xGe_1-x alloy at the interface which acts as a passivating layer. TEM, Raman and X-ray Photoelectron Spectroscopy studies confirm the formation of the core-shell structure with polycrystalline Ge as core and amorphous Si as shell without any germanium oxide formation. Given the inherent structure of metalattices, there are different degrees of confinement at octahedral, tetrahedral and meta-bond site. We are currently studying this spatial band gap modulation using electron energy loss spectroscopy. This understanding and control of metalattice surface along with the spatial structural modulation will enhance their tunability for desired properties and will also enable their applications in opto-electronic devices.
This work was supported by the National Sciences Foundation Materials Research Science and Engineering Centers (MRSEC) under award DMR-1420620.

1.Baril, N.F.; He, R.R.; Day, T.D.; Sparks, J.R.; Keshavarzi, B.; Krishnamurthi, M.; Borhan, A.; Gopalan, V.;Peacock, A. C.; Healy, N.; Sazio, P. J. A.; Badding, J. V. J. Am. Chem. Soc. 2012, 134, 19– 22

2. Han, J. E.; Crespi, V. H. Phys. Rev. Lett. 2001, 86, 696– 69

3.Russell, J.L.; Noel, G.H.; Warren, J.M.; Tran, N.L.L.; Mallouk, T.E. Langmuir 2017, 33, 10366– 10373

Particle-based crystallization relies on the synthesis and self-assembly of large numbers of monodisperse particles with nano to microscale dimensions. The fabrication of particles with diverse structures remains a challenge. Currently, inorganic nanoparticles with simple geometries (e.g. spheres, cubes, platelets) can be fabricated through bottom-up synthesis, while microscale Janus and patchy particles can formed through templating techniques. It is of interest to form lower symmetry shapes in which the direction of particle-particle interactions can be defined arbitrarily, and particle geometry can be used to precisely tune interparticle forces such as depletion forces. For instance, particles with one or more concavities (e.g. cube with concavities on 1 to 6 faces) can be combined with convex structures (e.g. spheres) to form complex self-assembled structures in 1D, 2D or 3D networks using lock and key mechanisms.

Here, we address the challenge of fabricating colloidal particles with complex geometries by using 2-photon lithography to 3D print microscale particles of arbitrary shapes. This method has been used to print hollow cones, spheres, cubes, tetrahedra, and dumbbells with bounding box dimensions of 5 um x 5 um x 5 um out of a fluorescent photoresist, and can be extended to other structures. In this method, a focused 780 nm laser is used to directly write a freestanding 3D structure into liquid photoresist, or within photoresist at the interface with a solid substrate. The particles are then transferred to a microfluidic cell, and in-situ fluorescence imaging is used to observe the dynamics and final configurations of the assemblies that form from these 3D printed particles. These 3D printed particles (e.g. concave particles) will be combined with traditional particles (e.g polymer or silica spheres) to form networks of multi-particle assemblies with controlled porosity, with the ultimate goal of forming periodic lattices with millimeter dimensions.

Epitaxially connected colloidal quantum dot superlattices with long-range atomic coherence have generated significant interest by virtue of their predicted emerging electronic properties. Whereas advances in controlled assembly and attachment at fluid-fluid interfaces have enabled the formation of high-fidelity superlattices in which constituent lead salt quantum dots are registered to within a single atomic bond length, significant gaps in our understanding of the fundamental mechanism underlying this transformation persist. The transformation involves a complex choreography of a number of sub-processes including: (i) the transport of a chemical trigger from the subphase to the quantum dot surface, (ii) the formation and removal of the ligand metal chelation complex, (iii) the rotation and translation of the quantum dots from their site in the initial assembly and (iv) the irreversible formation of an epitaxial bond between proximate dots through mutually exposed facets. What is astonishing and not yet understood is how the irreversible attachment of tens of thousands proximate dots are coordinated to enable the formation of micrometer-sized grains. Our recent experiments sought to capture intermediates of this intriguing transformation and revealed the existence of transient elongated structures along the <100> axis. New insights into the underlying processing-structure relationships coupled with computational simulations provide new understanding of the transformation mechanism. Beyond the specific model system of lead salt quantum dots discussed in this work, we expect that these new mechanistic insights will also provide valuable guidance to advance controlled assembly and attachment of related nanostructures.

Until recently, the vast majority of functional materials organizations at the nanoscale have been based in studies of packed nanoparticle architectures. Rationally designed, periodic structures tailored towards enhancing the local environment for chemical or biological components are far less explored, but equally important in consideration of their optical, catalytic, and enzymatic applications. The ability to separate material function from binding parameters bridges the divide between nanoparticles and a vast materials space often exhibiting anisotropic structure. A universal platform enabling novel hierarchical assemblies can be achieved utilizing DNA constructs that carry a molecular or nanoscale material object, where different units can be encoded for location within a crystalline lattice as well as for material type. Three-dimensional, hierarchical architectures allow for precise control of locally-defined material stoichiometries at the nanoscale as well as their mesoscale arrangements, encoding the position of units over multiple coordination spheres. With this capability, novel research into 3D structure-function relationships can be explored, as demonstrated optically using quantum dot organizations and chemically utilizing catalytic enzyme systems.

One-dimensional nanowire-based structures enable sophisticated design and integration of functional electrical components for modern electronics and devices. Recent developments in nanowire miniaturization have the potential for the next level of advanced assembly and packaging, but thus far engineering of nanostructures has been limited by associated challenges of interconnection. This work presents a core/shell multi-segment nanowire which achieved macroscale interconnection via magnetically assisted assembly and soldering. Gold-nickel-gold (Au-Ni-Au) nanowires were synthesized via electrodeposition in anodic aluminum oxide (AAO) template, with nickel acting as a magnetic vehicle for assembly. Gold-selective deposition of tin was achieved via establishment of a chemisorbed nickel-protective monolayer, followed by immersing the nanowires in aqueous solution for selective chemical reduction. This resulted in seeded tin deposition along the gold tips, which were subsequently grown into a coherent shell on gold. Core-shell formation was confirmed by SEM, TEM, EDS and XRD. These “dumbbell” shaped core/shell nanowires were assembled tip-to-tip and subsequently soldered, establishing ohmic electrical and thermal interconnection. This work establishes an effective and scalable method for site-specific nanowire functionalization while simultaneously addressing miniaturization-associated assembly and packaging issues in its desired applications.

We present applications of the flow coating methods to achieve unique and complex shapes of patterns or structures.
Flow coating is one of the solution coating techniques that exploit the coffee-ring effect. The coffee-ring effect is referred to a circle of a non-volatile solute that is left by a droplet of the solvent after it evaporates from a flat surface. It can be fund after coffee drop dries on a table.
This pattern originates from the capillary flow, which is induced by the different evaporation rates between the edge and center of the droplet. A flow coater is confined to the position of the droplet with the blade at a specific position, and the solute is deposited along the shore.
In this study, we combined such a simple phenomenon with different materials such as a polymer, silica particle, and organic semiconductors. Every material had proper conditions for flow coating from the solvent to the speed of the coating process. By control the factors, we could achieve various kinds of patterns without complicate process compare with other methods and determined the relationships between the control value and phenomenon.
First, the relationship between stopping time of flow coater and deposition phenomenon of several times of patterning process was investigated. Stopping motion of blade of flow coater gave more deposition of solute, and it could make thick or wide patterns. The difference of pattern’s height impacted the additional patterning mechanism on the patterned surface. Height of patterns inhibited deposition of solute on its top inducing a dewetting phenomenon. We could observe a change of height with a dewetting phenomenon and the amount of deposition rate with the shape of patterns. Various kinds of non-linear dewetting induced patterns are reported in this study.
Second, the relationship between the speed of flow coater and deposition phenomenon such as height and structural morphology of the film was explained. Speed of flow coating process is one of the critical factors that can control the amount of evaporating solvent. , flow coating could control the overall thickness, and it spontaneously changed along with the speed of the blade. In this study, nano-sized silica particles was deposited on the substrate, affording a closely packed, well-ordered structure. Photonic structures were achieved in the same manner. The thickness of photonic crystal was changed along with the speed and photonic property was examined.
Third, the relationship between the speed of flow coater and shear stress on the solution was determined with organic conducting materials. The flow coating system basically comes from solution shear coating method and the shearing gives shear stress on the solution. Shear stress deformed crystal structures and it made conducting property differently.
The patterns that came through flow coating had various shapes and its application and they were easy to obtain. Compared to other methods, flow coating is an important method due to the following reasons. First, lithography or nano-casting needs complex steps to achieve a photonic structure, while flow coating does not need a developed process. Second, deep coating takes a long time until the liquid evaporates to form a thick film. However, flow coating overcomes such problems and exhibits more advantages.

Optogenetics is a field of study that combines optics and biology to control living tissues via light sensitive proteins (opsins) and radiative energy. Traditionally, optical fibers are used as a waveguide to introduce light pass the cranial; consequently, this has negative side effects such as localized heating and surgical scars. Here a noninvasive technique is proposed utilizing a high penetrating and low tissue attenuation x-ray excitation source and nanoparticulates that scintillates to deliver radiative energy to light sensitive proteins.
Scintillators are a class of materials that can experience a downconversion of electrons from a high energy excitation source, such as x-rays. The ideal scintillators utilized in radiation detection have a high atomic number, high density, inert, and have discrete emission behaviors suitable for its end use. Typical non-toxic and high light output scintillators that can be applied in the biomedical field are silicate materials which are synthesized at temperatures above 1000^oC; as such the synthesis of sub 100 nm scintillators is a challenge not fully explored yet due to the difficulties from sintering.
Two polymorphs of the Re₂Si₂O₇ (Re = Y³⁺ or Lu³⁺) were crystallized at the nanoscale at above 1000^oC while remaining monodisperse particulates. A core bishell architecture was used as a physical and chemical template composed of a SiO₂ core and a Re₂O₃ shell, followed by polymerization of a secondary pDVB shell, on the inorganic core-shell particulate. The organic coating carbonized to amorphous carbon at conventional sintering temperatures preventing particle-particle contact and was easily removed. Furthermore different lanthanide dopants (Ce³⁺, Tb³⁺, and Eu³⁺) were incorporated into the particulates that can couple to different opsins. The sacrificial amorphous carbon process demonstrated control over structure-luminescent properties that can potentially be used for non-invasive optogenetics. The two atypical fields of organic and inorganic chemistry provided complementary abilities that were instrumental into the development of the high temperature nanoreactor and has the potential to be expanded upon to different crystals.

The nascent ability to convert biological self-assembled lattices from DNA-origami nano-objects into finely-templated inorganic replicas compel us to explore how defects form in this unique class of material in order to engineer future motifs. However, little is known of the internal landscape of superlattices due to limitations from optical, x-ray, and electron microscopy techniques. Our pioneering effort delves beneath the surface of crystals by leveraging advances in non-destructive x-ray microscopy to examine internal defects, dislocations, and grain boundaries associated with different origami motifs. We also utilize destructive imaging to unveil an order-of-magnitude greater volumetric data using focused ion beam serial sectioning. Defects and dislocations within these structures reveal stark connections to atomic theory while retaining biological origins.

One dimensional (1D) nanomaterials are well recognized as the promising building blocks for nanoscale devices and systems in the post-Moore era. The past decades have witnessed rapid advance in scalable growth of various 1D nanomaterials with tight control of physicochemical properties. However, precise positioning of the individual 1D building block to form well-organized three dimensional (3D) nanostructures with high designability and positioning accuracy remains a daunting challenge. In this talk, we will firstly make a brief overview of the progress in controlled assembly of 1D nanomaterials including the post-growth assembly and in-situ growth strategies, respectively. Then a newly-developed method of femtosecond laser induced assembly will be introduced. Various functional 1D nanomaterials including carbon nanotubes, ZnO nanowires and silver nanowires were systematically studied and assembled using the ultrafast laser direct writing technique with about 100 nm spatial resolution. The dependence of assembly parameters on the size of 1D nanomaterials, scanning speed, laser power and the inherent assembly mechanism were also discussed. The laser induced assembly not only demonstrates high positioning accuracy and wide material applicability, but also enables the alignment control of 1D nanomaterials in 3D assembly process. The laser-based strategy opens a route for advanced nano-device fabrication which will benefit numerous emerging fields including 3D electronics, integrated photonics, and MEMS/NEMS.

Metal particle catalyzed semiconductor nanowire growth, or vapor-liquid-solid (VLS) growth, is a highly promising route to one-dimensional hierarchical materials. The most common catalyst particle material for III-V nanowires is gold and growth of such nanowires can be carried out in a variety of epitaxy set-ups, such as metal organic vapor phase epitaxy (MOVPE) and molecular beam epitaxy. Aerotaxy is a relatively new growth method that admits growth of nanowires without substrates, directly in the vapor phase at very high growth rates [1].

In this presentation, we propose a model for the length growth rate of nanowires grown by means of the VLS mechanism. Our model is based on deposition-diffusion-desorption-incorporation kinetics in steady state, and using this model we discuss nanowire growth in two experimentally relevant limits: mass transport limited growth and incorporation limited growth. We discuss our modelling results in view of experimental nanowire growth results with a special emphasis on the radius-independent, incorporation limited growth rate in the high pressure limit, observed under specific, extreme conditions of nanowire growth which are reached during aerotaxy growth. Based on diffusion calculations, we find it plausible that these growth rates are indeed the maximum growth rates under the given conditions.

Moreover, in the mass transport limit, our model explains nanowire growth in MOVPE. Specifically, we explain the experimental observations of the V/III ratio dependence of the nanowire growth rate, observed by Soci et al. [2]. According to our model, the higher the group V pressure, the more linearly does the growth rate depend on the group III pressure. In this well-known limit, the growth rate is proportional to the group III pressure and the surface diffusion length of group III material along the nanowire and inversely proportional to the nanowire radius. On the other hand, in the limit of low group V pressures the growth rate becomes independent on group III pressure.

If both the group III and the group V pressures are sufficiently high, the nanowire growth rate is at its maximum and is limited by the incorporation kinetics. In this regime the growth rate depends only on temperature but not on pressures. It might be that some processes operate at unnecessarily high pressures so that significantly decreasing the pressures would not lead to a decrease in the growth rate. Therefore the insights from our modeling not only provide valuable insights in mass transport limited growth, but could also be used to reduce the cost of some processes, where the aerotaxy process is one possible example.

[1] M. Heurlin, M.H. Magnusson, D. Lindgren, M. Ek, L.R. Wallenberg, K. Deppert, L. Samuelson, Continuous gas-phase synthesis of nanowires with tunable properties, Nature 492 (2012) 90-94.
[2] C. Soci, X.Y. Bao, D.P.R. Aplin, D.L. Wang, A Systematic Study on the Growth of GaAs Nanowires by Metal-Organic Chemical Vapor Deposition, Nano Lett. 8 (2008) 4275-4282.

Light-weight aerogel materials hold great promise for thermal insulation. However, its low mechanical integrity and high-cost manufacturing hampered its progress for large-scale adoption in energy-efficient building insulations. In addition, it is indispensable for thermal management to achieve more soundproof and heat-resistant characteristics. In this study, we design and synthesize the scalable pore-gradient ceramic aerogel monoliths (PGAeros) through the biomimetic approach. The low-cost manufacturing of PGAeros is further facilitated by the in-situ gas bubble formation to support the pore gradient. The PGAeros exhibit a robust mechanical and thermal stability across a broad temperature range (0.040 W m⁻¹ K⁻¹, and a compressive strength of 100.56 MPa, respectively). The design of thermal regulation in such PGAeros is inherited from the human skin concept, where the pore gradient regulates the thermal management over the seasons. The integral ceramic monolith nature provides such PGAeros with robust soundproof and fire-resistance performance. The demonstration of scalable manufacturing of bio-mimetic inspired ceramic aerogel materials opens up thermal insulation applications with remarkable thermal management, high mechanical strength, low mass density, superior soundproof and fire-retardant performances.

Colloidal and nanoparticle systems exhibit novel and unexpected phase behavior including the self-assembly of highly complex crystal structures. The inverse design of pair potential models provides a promising route for the a priori approximation of required particle interactions for the targeted self-assembly of unique colloidal crystal structures. State-of-the-art techniques for the optimization of isotropic pair potentials tend toward overfitting, resulting in solutions with many features on different length scales that are challenging to map to mechanistic models. Here, we demonstrate how to effectively steer the optimization of pair interactions toward smooth, simple and possibly realizable solutions by amplifying relevant frequencies within the Fourier spectrum of the pair potential function. The resulting simpler functions should not only be more readily transferable to experiments, but simulated self-assembly pathways are generally also more robust and less prone to vitrification.

Mixed transition-metal oxides (MTMO) are materials that its structural configuration consists in oxides with two different cations as AxBYOZ (where A and B are transition metals). This arrangement allows a several possibilities of structures and improve properties. The synergistic effect of multiple cations valences can to increase properties like, high conductivity and electrochemical activity, which contribute for uncounted applications, mainly in energy storage devices. Between metal oxides, ruthenium oxide (RuO2) has been used, owing excellent electrochemical properties, such as wide electrical potential range, high conductivity and specific capacitance. However RuO2 shows many disadvantages, it is expensive and toxic, reducing severely its application. An interesting alternative is focused on the combination of RuO2 with other materials, like metals or oxides,decreasing amount of Ru in the oxide. In this way, we combined ruthenium with tungsten oxide (WO3), in order to obtain a novel MTMO. WO3 is excellent candidate, due his unique properties. The development of novel MTMO structure (RuxWyOz) was based on bottom up strategy, using a modified polyol method, with a triblock polymer (Pluronic 123) as surfactant and different metal chlorides salts as precursors. Different precursors ratios were evaluated in order to obtain the better results. The nanomaterial obtained as characterized by different techniques such as, Raman and energy-dispersive X ray spectroscopy, scanning electron and atomic force microscopy. These analyses ensure the successful of material synthesized and shown the mainly properties of this new MTMO. RuxWyOz thin films were also characterized by electrochemical techniques, exhibiting superior capacitive performance when compared to control samples (RuO₂ and WO₃). The results show promising application in energy storage field. Authors acknowledges Mackenzie Presbiterian Universisty (UPM), FAPESP (2018/02142-0, 2017/21988-5 and SPEC2012/50259-8), CNPq (403544/2016-5), Materials Chemistry Group (GQM – UFPR), LNNano and INCT of Carbon Nanomaterials.

The laser damage behavior of three-dimensional photonic crystals (3D-PCs) with an opal structure is investigated using both experimental and simulation methods. Polystyrene (PS) colloidal crystals films with a reflection peak at 1064nm are used as the model material. Disordered films (DF) are fabricated with PS microspheres as contrast samples. The laser-induced damage threshold (LIDT) of 3D-PCs is tested, which is as 2.35 times high as the LIDT of DF. All laser damages are derived from defects in 3D-PCs, implying that the LIDT of ideal 3D-PCs will be significantly increased. The simulation results show that the electric field is contained in the pores of 3D-PCs while it is reduced in the PS microspheres, which may decrease the absorption of laser energy by 3D-PCs. In contrast, the electric field distribution is irregular in DF. Enhanced electric field areas are located in both the pores and microspheres of DF. Considering higher electric field intensity causes more energy absorption and higher temperature, the DF have a lower LIDT. The 3D-PCs structure uses ordered vacancy to contain and strike back laser energy and can increase the LIDT without changing the chemical composition of materials.

Traditional small molecule supramolecular assemblies (e.g. in natural systems like lipid membranes or those derived from peptides) generally exhibit high molecular exchange rates, molecular migration, and other dynamic instabilities. These dynamic processes may be beneficial for the application of supramolecular materials in biological environments, but the ability to increase nanostructure stability might provide a path forward for their application in non-biological applications. Here, we present the design of small molecule amphiphiles fabricated with robust intermolecular interactions which self-assemble into ultra-stable supramolecular nanofibers. These nanofibers notably maintain both the self-healing characteristics found in traditional amphiphilic systems and exhibit unique mechanical and thermal stabilities that arise from the tunable intermolecular interaction strengths within each assembly. Taking advantage of the high aspect ratio of these nanomaterials, heavy metal chelators are rationally chosen for expression in high densities on the nanofiber surfaces. We demonstrate the capacity for significant remediation of heavy metals from water using this novel class of materials with orders of magnitude improvement over macroscopic alternatives in use today.

Direct detection of DNA by surface enhanced Raman spectroscopy has shown great advantages and potentials owning to its ability to provide intrinsic chemical information of DNA molecules themselves with a high sensitivity. However, much small Raman scattering cross section of DNA molecules causes the SERS spectra hard to be collected directly and the SERS spectra were found to be dominated by the vibration of adenine. Although various methods of direct DNA detection by surface enhanced Raman scattering (SERS) have been proposed, more reliable and more stable SERS platform with higher signal-to-noise ratio still requires.
In this study, we propose an evaporative self-assembly strategy for constructing long-life 3D SERS hotspot matrix with the assistance of glycerol to improve the spectral sensitivity and reproducibility in direct DNA detection. Silver nanoparticles (AgNPs) are dispersed in mixed solvents that contain a small amount of non-volatile solvent glycerol and volatile solvent water. Additionally, Mg²⁺ is introduced to the AgNPs colloids to construct the sandwich structure (AgNPs-DNA-AgNPs) between negative charge AgNPs and phosphate backbones through electrostatic interaction. When the droplet is dried on a hydrophobic silicon substrate, water evaporates rapidly and glycerol as a non-volatile solvent creates a liquid environment that can stop the AgNPs colloids turning into the drying state. Both AgNPs and DNA will be concentrated and assembled together to form a 3D AgNPs hotspot matrix at the silicon/glycerol solid-liquid interface. Brownian dynamics simulations reveal that more hotspots turn up in the glycerol-stabilized 3D AgNPs hotspot matrix and the distances between the AgNPs in the liquid environment are not fixed but balanced in a small range by the interplay of the van der Waals attraction and the electrostatic repulsion. Two orders of magnitude extra SERS enhancement, more stable peak frequencies and narrower peak full width at half maximum (FWHM) can therefore be obtained, which enable the direct detection of both single strand DNA (ssDNA) and double strand DNA (dsDNA) with stable, reproducible and reliable signal-to-noise ratio SERS signals. Using the symmetric stretching vibration peak of phosphodioxy (PO²⁻) at 1087 cm^-1 as the intensity internal standard, we are able to quantitatively determine the base content in oligonucleotides with single base sensitivity.
This fascinating evaporative self-assembly strategy opens up a novel perspective in manipulating plasmonic nanoparticles to construct the SERS platforms at solid/liquid interface. Ultrahigh spectral sensitivity and reproducibility of the glycerol-stabilized 3D SERS hotspot matrix would promote the surface enhanced Raman spectroscopy to become a more practical and reliable tool in direct DNA detection and analysis.

Cellulose is ubiquitous in our everyday life from our homes to our offices. Cellulose nanocrystals (CNCs) that can be obtained from different cellulose sources are rod-like nanoparticles with dimensions on the order of a few hundredth nanometer in length and a few nanometers in widths. When dispersed in water CNCs behave like a lyotropic liquid-crystal and give rise to either isotropic or anisotropic suspensions. Whereas drying an isotropic suspension (low CNC concentration) yields transparent films, interesting photonic properties (iridescence) can be obtained by drying an anisotropic suspension (CNC concentration > 2 wt%), owing to a twisted ordering on the nanoscale. This ordering is due to an evaporation induced self-assembly process and is referred to as a chiral nematic structure.
In this work we report on the integration of bio-inspired chiral CNC memranes into sensing devices with distinct sensing properties for left- and right-handed circular polarized light (LCPL and RCPL, respectively). The CNC films are employed as photonic dielectrics in oxide thin films transistors and light filters in amorphous silicon photodetectors with the capability of discrimination between LCPL and RCPL signals in the visible region.
<!--![endif]---->

Surface-enhanced Raman Spectrometry (SERS) based on localized surface plasmon resonance can recognize strong Raman signals highly specific to a chemical molecule by great analytical performances. SERS enhancement factor (EF) majorly relies on distribution and density of hotspots regarded as nanoscale gap distances among noble metal nanoparticles; increasing EF necessitates a sophisticated nanostructure, either two-dimensional arrangement or three-dimensional (3D) structuring. Cellulose fibril substrates demonstrate so highly porous network structure that researchers have investigated it for development of cellulose-based SERS platforms. However, the perpendicular distances between the fibrils exceed upon micrometers resulting in low reducibility and EF level. While numerous ensuing researches have attempted to fabricate nanopatterned structures, these methodologies required highly pricey equipment and intricate processes.
Herein, we demonstrate 3D plasmonic nanostructure built on cellulose fibril surfaces using Layer-by-Layer technique. The fabricating procedure consists of steps alternatively dipping a cellulose substrate into each solution respectively containing positively and negatively charged materials; silver nanoparticles were synthesized via in-situ reduction method with capping negatively charged molecules, and a positively charged chitosan derivate oligomer was employed for the fabrication. Structural parameters were deliberately adjusted by the stepwise methodology and changes in chemical reagents concentration. Optical and mechanical traits, and surface chemistry of the substrates were altered with accordance to increasing generations. Transverse routes of analytes were confirmed by morphological studies associated with energy dispersive X-ray spectroscopy mapping. In the analytical application, the SERS substrate demonstrated a gainful performance with bringing about respected EF, limit detection, and reproductivity.
This 3D plasmonic structure was sophisticatedly built on the cellulose microfibrils and revealed profitable functions when applied to SERS analysis. It achieved high reproductivity and sensitivity without engaging complex and costly fabricating procedure. Thus, this Multilayered SERS platform is potentially advantageous for numerous purposes, in particular for point-of-care diagnosis.

Light-harvesting complexes in nature consist of disk-coil motifs, a chlorin- or porphyrin centered molecule with functionalized alkyl chain. Of the many light-harvesting complexes, bacteriochlorophyll (Bchl) is of special interest due to its role in particular bacteria living in a low light environment. Bchl is the building block of chlorosome, a large light-harvesting antennae complex that allows the bacteria to harvest energy efficiently from the low-light environment. It is believed that Bchl gives chlorosome such high light-harvesting abilities due to the molecule self-assembling based on bchl-bchl interaction, which differs from chloroplast, the light complex in green plants that self-assembles from chlorophyll-protein interaction. In Bchl, the dominating features that allow the bacteriochlorophyll to form the light harvesting complex are believed to be the metal core of the porphyrin, OH group, and the long alkyl chain. This allows a combination of hydrogen bonds, coordination bonds, and π-π interactions to occur between the disk coil motif which enables assembly into the light-harvesting complex. Hence, studying the self-assembly behavior of disk-coil motifs is essential to reproduce the self-assembled structure of chlorosome that may govern its photosynthetic performances. In this study, we synthesized a disk-coil motif that mimics the bacteriochlorophyll molecule. The disk-coil motif was designed with a porphyrin-based disk that accommodates the key features that are believed to allow bacteriochlorophyll to self-assemble in the confined environment. From this, the self-assembly properties of this structure were studied to understand the self-assembly of disk-coil structures.