Tuning of Thermal Back Reactivity of Aza-Diarylethene Photoswitches by Introducing Benzazole Groups

Molecular photoswitches have attracted significant attention due to their potential applications in materials science and life science. In this study, we synthesize a series of aza-diarylethenes incorporating benzazole groups as the nitrogen atom source for 6π azaelectrocyclization and investigate their photochromic behaviors. Compounds 1-3, bearing benzothiazole, benzoxazole, and benzimidazole groups, exhibit thermally reversible type photochromism with thermal back reaction half-lives (t_1/2) ranging from milliseconds to seconds at 293 K. Additional derivatives 4-6 with benzothiophene-S,S-dioxide at the ethene bridge moiety further expand the range of thermal back reactivity, with t_1/2 values extending up to tens of minutes. Quantum chemical calculations confirm that the variation in thermal back reactivity is governed by the energy difference between open- and closed-ring isomers, in accordance with the Bell-Evans-Polanyi principle. These findings provide a molecular design strategy for controlling the thermal back reactivity of aza-diarylethenes, enabling further development of functional photochromic materials.