Controlled Sol–Gel Transitions of a Thermoresponsive Polymer in a Photoswitchable Azobenzene Ionic Liquid as a Molecular Trigger

Producing ionic liquids (ILs) that function as molecular trigger for macroscopic change is a challenging issue. Photoisomerization of an azobenzene IL at the molecular level evokes a macroscopic response (light‐controlled mechanical sol–gel transitions) for ABA triblock copolymer solutions. The A endblocks, poly(2‐phenylethyl methacrylate), show a lower critical solution temperature in the IL mixture containing azobenzene, while the B midblock, poly(methyl methacrylate), is compatible with the mixture. In a concentrated polymer solution, different gelation temperatures were observed in it under dark and UV conditions. Light‐controlled sol–gel transitions were achieved by a photoresponsive solubility change of the A endblocks upon photoisomerization of the azobenzene IL. Therefore, an azobenzene IL as a molecular switch can tune the self‐assembly of a thermoresponsive polymer, leading to macroscopic light‐controlled sol–gel transitions.