Porous liquids are a new class of functional material that combines the mobility of a liquid with the properties of a porous solid. This combination means they have unique applications, such as the ability to be pumped around a continuous system, facilitating guest loading and unloading steps. Porous liquids fundamentally differ to conventional liquids in that they contain permanent, empty, accessible cavities. By engineering ‘intrinsic’ porosity into a liquid; that is, by incorporating permanent shape-persistent cavities within the molecules that make up the liquid, over the inherent ‘extrinsic’ porosity seen in all liquids, it is possible to form a porous liquid. Three types were initially proposed in 2007 broadly defined as: Type I – a neat liquid porous material containing rigid internal cavities, Type II – a porous material dissolved in a cavity-excluded solvent, and Type III – a porous material dispersed in a cavity-excluded solvent. However, it was only from 2015 onwards that the first porous liquids were reported which provided proof-of-concept that permanent porosity in liquids was achievable. The main challenge in developing porous liquids is maintaining the porosity of the solid whilst rendering it into a liquid state. To take one example, porous organic cages (POCs) are discrete molecules that contain permanent molecular cavities, making them ideal candidates with which to generate porous liquids. However, typically, POCs thermally decompose before melting, or have low solubility, meaning a number of design strategies were required in order to successfully use them in the formation of porous liquids. For example, to address the low solubility, the formation of highly soluble vertex-disordered ‘scrambled’ cage mixtures was utilized to form type II porous liquids, which exhibited certain properties that are well defined for microporous porous solids such as gas uptake and guest selectivity; occupancies as high as 72% and 74% were observed for Xe and SF6 respectively, and larger guests were size-excluded from the cage, whilst smaller guests could enter the cage cavity and displace encapsulated gases. Recent advances include gaining a more in-depth understanding of these systems, the synthesis of new POC based porous liquids that exhibit higher pore concentrations and gas selectivity, and investigation of their potential use in new applications.

Advances in porous liquids formed using porous organic cages

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.