Light-Controlled Exposure/Blockage of Permanent Cavities in Metal-Organic Cages-Based Type II Porous Liquids

Photoresponsive porous liquids (PPLs) have garnered increasing attention due to their ability to controllably modulate gas uptake upon light irradiation. Currently, the modulation on gas uptake of reported PPLs is based on configuration transformation of photoresponsive motifs, while their permanent pores remain unchanged. Here we report for the first time the fabrication of type II PPLs with adsorption capacities tunable by light-controlled exposure/blockage of permanent cavities. The charged metal-organic cage (MOC-SO₃Na) is modified by 3-phenylazopyridine ligands on metal open sites, producing a new photoresponsive porous host MOC-SO₃Na-Azo (MSA). A phosphorus-containing bulky ionic liquid, [P_6,6,6,14][Cl], provides electrostatic interactions that enable the dissolution of MSA with high solubility (70 mg mL^-1). The obtained type II PPL, PPL-MSA, shows CO₂ uptake (9.9 cm³ g^-1 at 25°C, 1 bar) much superior to all reported type II porous liquids (0.2-3.0 cm³ g^-1). Under different light conditions, PPL-MSA demonstrates 49.3% change in CO₂ uptake, which is obviously higher than the porous host (7.6%) and solvent (0.3%). This photoresponsive efficiency is attributed to exposure/blockage of permanent cavities within PPL-MSA.