Ion-selective response of visible light photoswitchable indole-hemithioindigo: toward chemical sensing of fluoride and hydroxide.

The chemical sensing of hydrophilic anions such as F - and OH - is of significant importance but also presents considerable challenges. Herein, the thermal E to Z isomerization of a visible-light-responsive photoswitch (HTI-In) is utilized to address this challenge for the first time. The isomerization of HTI-In is dependent on the concentration of F - and OH - , and exhibits excellent selectivity toward F - and OH - over other common anions and cations. Unlike irreversible chemodosimeters and other conventional fluorescent probes, the photodynamic sensing of F - and OH - (demonstrated in solvents and polyurethane hydrogels) is based on a non-equilibrium chemical kinetics and can be operated fully reversibly.