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.