Entropy-Driven Porous Liquids Allowing Gas Solubility in Solvent-Filled Imine-Based Porous Organic Cages

Porous liquids offer
a promising platform for gas separation by
combining fluid processability with intrinsic molecular porosity.
Traditional Type II porous liquids are formed by dissolving porous
molecular cages in size-excluded solvents, limiting solvent options
and practical applications. In this work, we introduce a novel method
of creating Type II porous liquids using common small solvents, where
intrinsic porosity is achieved at elevated pressures due to the selective
displacement of solvent molecules by gas molecules within the cage
structures. Using molecular simulations, we investigate the behavior
of CO2 in solutions of the imine-based porous organic cage
CC13 dissolved in small molecular solvents such as chloroform and
1,2-dimethoxyethane (DME). Grand canonical Monte Carlo simulations
of solid-state CC13 reveal that selectivity reversal, where smaller
CO2 molecules displace larger solvent molecules inside
the cage, is achievable at sufficiently high pressures. Temperature
quench molecular dynamics simulations confirm that while CO2 displacement within chloroform-filled cages is limited, DME enables
entropy-driven cage CO2 occupancy at pressures as low as
∼23 bar, setting up the foundation of an alternative way of
forming Type II porous liquids.