Visible‐Light‐Driven Solid‐State Fluorescent Photoswitches for High‐Level Information Encryption

Developing visible‐light‐driven fluorescent photoswitches in solid state remains an enormous challenge in smart materials. Such photoswitches are obtained from salicylaldimines through excited‐state intramolecular proton transfer (ESIPT) and subsequent cis‐trans isomerization strategies. By incorporating a bulky naphthalimide fluorophore into Schiff base, three photoswitches achieve dual‐mode changes (both color and fluorescence) in the solid state. In particular, the optimal one generates triple fluorescence changing from green, to yellow and finally orange upon visible light irradiation. This switching process is fully reversible and can be repeated at least 10 times without obvious attenuation, suggesting its superior photo‐fatigue resistance. Mechanism studies reveal that naphthalimide group not only enables the tuning of multicolor with an additional emission, but also induces a folded structure, reducing molecular stacking and facilitating ESIPT and cis‐trans isomerization. As such, photopatterning, ternary encoding and transient information recording and erasing are successfully developed. The present study provides a reliable strategy for visible‐light‐driven fluorescent photoswitches, showing implications for advanced information encryption materials.