Precisely Modulated Photoresponsiveness of Porous Liquids via Azobenzene Orientation Engineering

Photoresponsive porous liquids (PPLs) are emerging as promising materials for light-regulated gas adsorption, while precise control over their photoresponsiveness remains challenging. Herein, we report precise modulation of the PPLs’ photoresponsiveness by azobenzene orientation engineering in the hosts. Two positional isomers, 4-phenylazopyridine (4-Azo) and 3-phenylazopyridine (3-Azo), are anchored onto the axial metal sites of a sulfonate-containing metal−organic cage (MOC), affording porous hosts MOC-4-Azo and MOC-3-Azo with distinct azobenzene orientation. Considering the anionic nature of hosts, a polyethylene glycol-based ionic liquid (IL-Br) is designed as a sterically hindered solvent, yielding two PPLs, PL-4-Azo and PL-3-Azo. Notably, PL-4-Azo shows a 49.5% change in propylene uptake under light irradiation, whereas PL-3-Azo shows only a 1.0% variation. This pronounced difference originates from the different spatial orientations of azobenzene, which influence its ability to regulate internal and external cavities upon isomerization. This study may provide insights into precise design of stimuli-responsive materials for various applications.