Diarylethene Photoswitches Undergoing 6π Azaelectrocyclic Reaction: Disrotatory Thermal Cycloreversion of the Closed-Ring Isomer.

Gaining insight into the dynamics of electrocyclic reactions is very important from both fundamental and application perspectives. In this study, we developed novel diarylethene photoswitches that undergo 6π azaelectrocyclic reaction. We found that they exhibit fast thermally reversible type (T-type) photochromism, in contrast to the fact that common diarylethenes exhibit photochemically reversible type (P-type) photochromism. The quantum chemical calculations revealed that the fast T-type photochromism originates from the unprecedented disrotatory thermal cycloreversion of the closed-ring isomer. Our results provide useful information not only for the dynamics of the 6π azaelectrocyclic reaction but also for the further development of diarylethene photoswitches utilizing the 6π azaelectrocyclic reaction.