Abstract Photo-induced tuning of lower critical solution temperature (LCST) behavior is an attractive route for reversible phase control, yet the achievable cloud-point shift is often modest in conventional solvent systems. Here, we demonstrate a composition-amplified, light-tunable LCST in ionic liquid polymer solutions using random copolymers of 4-phenylazophenyl methacrylate and phenethyl methacrylate (P(AzoMA- r -PhEtMA)) dissolved in 1-ethyl-3-methylimidazolium trifluoromethylsulfonylimide (C 2 mimTFSI), a medium in which the azobenzene-containing monomer is readily compatible. Turbidity measurements reveal opposite cloud-point shifts under UV ( cis -type) and visible-light ( trans -type) conditions, enabling a bistable temperature window that widens monotonically with azobenzene composition. At 37 °C, the solution is reversibly switched between one-phase and two-phase states by light alone and maintains stable cycling for more than ~40,500 s. These results provide a practical molecular design guideline for targeting ambient-to-physiological light-controlled phase separation in nonvolatile ionic liquid media.
Naka et al. (2026) studied this question.