Control of pore window size is the standard approach for tuning gas selectivity in porous solids. Here, we present the first example where this is translated into a molecular porous liquid formed from organic cage molecules. Reduction of the cage window size by chemical synthesis switches the selectivity from Xe‐selective to CH4‐selective, which is understood using 129Xe, 1H, and pulsed‐field gradient NMR spectroscopy.

The dispersion of particulate porous solids in size-excluded liquids has emerged as a method to create Type III porous liquids, mostly using insoluble microporous materials such as metal-organic frameworks and zeolites. Here, the first examples of Type III porous liquids based on porous organic cages (POCs) are presented. By exploiting the solution processability of the POCs, racemic and quasiracemic cage microparticles are formed by chiral recognition. Dispersion of these porous microparticles in a range of size-excluded liquids, including oils and ionic liquids, forms stable POC-based Type III porous liquids. The flexible pairing between the solid POC particles and a carrier liquid allows the formation of a range of compositions, pore sizes, and other physicochemical properties to suit different applications and operating conditions. For example, it is shown that porous liquids with relatively low viscosities or high thermal stability can be produced. A 12.5 wt% Type III porous liquid comprising racemic POC microparticles and an ionic liquid, [BPy][NTf 2 ], shows a CO 2 working capacity (104.30 µmol g L −1) that is significantly higher than the neat ionic liquid (37.27 µmol g L −1) between 25 and 100 °C. This liquid is colloidally stable and can be recycled at least ten times without loss of CO 2 capacity.

The realisation of permanent microporosity in liquids transforms the way functional porosity may be implemented. Considering recent advances, we explore the developing theory of porous liquids and delve into the discovery process and applications.

Control of pore window size is the standard approach for tuning gas selectivity in porous solids. Here, we present the first example where this is translated into a molecular porous liquid formed from organic cage molecules. Reduction of the cage window size by chemical synthesis switches the selectivity from Xe‐selective to CH4‐selective, which is understood using 129Xe, 1H, and pulsed‐field gradient NMR spectroscopy.

Twin screw extrusion (TSE) is demonstrated as an alternative synthetic method for preparing a prolific porous organic cage.