From Porous Organic Cages to Porous Liquids: Translating Porosity from the Solid to Liquid State

The landscape of microporous materials is often dominated by crystalline, ordered materials. However, the development of microporosity in the liquid state is leading to an inherent change in the way applications of functional porosity are approached. Porous liquids combine the mobility of a liquid with the properties of a microporous solid, and fundamentally differ to conventional liquids in that they contain <i>permanent</i>, <i>empty</i>, accessible cavities. Four types of porous liquids have now been proposed: type I – neat molecular porous liquids; type II – solutions of molecular porous species in pore-excluded solvents; type III – dispersions of microporous solids in pore-excluded liquids; and type IV – neat meltable microporous extended frameworks. Like their solid counterparts, porous liquids are capable of both gas uptake and selectivity and demonstrate increased gas solubility compared to conventional liquids. However, this combination also means porous liquids offer unique properties and applications when compared to porous solids, such as the ability to be pumped around a continuous system, facilitating guest loading and unloading steps. Our recent work in the area, with a focus on translating porous organic cages - discrete shape-persistent molecules containing permanent molecular cavities accessible through windows – into different types of porous liquids using different strategies will be presented, alongside how we are attempting to streamline their discovery using a high-throughput workflow. The properties of the different porous liquids including gas uptake, guest selectivity, and controlled gas release, will also be discussed, touching on our recent work on incorporating a photoresponse into a porous liquid.