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

Developing visible-light-driven fluorescent photoswitches in the 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 a Schiff base, three photoswitches achieve dual-mode changes (both in color and fluorescence) in the solid state. In particular, the optimal one generates triple fluorescence changing from green, to yellow and finally to orange upon visible-light irradiation. This switching process is fully reversible and can be repeated at least 10 times without obvious attenuation, suggesting its good photo-fatigue resistance. Mechanism studies reveal that the 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.