Compact and Robust Scaffold for Visible-Light-Actuated Photoswitching

Photoswitches, molecules that toggle between isomeric forms upon electromagnetic irradiation, have important applications ranging from materials science to pharmacology. Currently, there is a need for photoswitches operated by visible light. We describe the synthesis and characterization of a new class of small-sized, push-pull photoswitches based on aryl azothiadiazole moieties, with excellent visible light switching performance and stable Z isomers. Photoconversion efficiency was found to be concentration-dependent, and we determined an optimal irradiation protocol at λ = 400/550 nm for bidirectional switching. All compounds displayed complex concentration-dependent switching kinetics, which we attribute to solvent interactions or aggregation phenomena in solution. Finally, we used computational chemistry to explain our observations related to absorption and activation barriers for the thermal Z → E back-isomerization. We anticipate that our novel photoswitches will be broadly useful in numerous instances requiring visible light control.