pH‐Induced Fluorescence and Thermal Relaxation Rate Modulation in a Hydrazone Photoswitch

A recently developed family of bistable hydrazone‐based photochromic compounds open new possibilities for molecular machinists with their unique combination of properties. Herein we report on the effect of acid/protonation on the switching and fluorescence emission of a recently reported dimethyl amino hydrazone derivative ( 1 ). The fluorescence of 1 can be turned ON/OFF upon deprotonation/protonation cycles, and protonated 1 photoswitches efficiently. Meanwhile, acid catalysis leads to a dramatic acceleration of its thermal relaxation rate (from years to hours).