Non-isomerizing switching strategy for azobenzene photoswitch

Azobenzene photoswitches serve as key building blocks for smart materials due to the controllable isomerization and machinability. However, traditional cis-trans isomeric azobenzene photoswitches are hindered by the thermal instability of the cis structure. In this perspective, we break the limitation by introducing an effective trans-azobenzene photoswitch strategy enabled through excited-state intramolecular proton transfer (ESIPT) in coordination with anti-Kasha fluorescence emission. The photoswitch exhibits a prominent reduction in quantum yield from 0.37 to 0.07 upon switching from the on state to the off state. Femtosecond transient absorption spectroscopy combined with quantitative computational methods elucidated ESIPT and anti-Kasha emission processes. The biological relevance of the design is demonstrated through in-cellular fluorescence modulation of 12 hours and 40 cycles in HeLa cells. By decoupling the photo function from structural rearrangement, we establish a design tactic for photoswitches.