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.