Light-responsive spiropyran derivative with tunable assembly morphology and solid-state photochromism for rewritable optical printing and multi-level anti-counterfeiting

Abstract

Light-responsive materials are attracting increasing scientific and technological interest due to their potential applications in data storage, optical printing, information encryption, anti-counterfeiting, chemical sensors, tunable assembly, and soft actuators. Here, a light-responsive tetraphenylethene (TPE)-modified spiropyran derivative SPD with tunable assembly morphology and solid-state photochromism is reported. The light-responsive behaviors of SPD have been carefully studied from monomeric state to aggregation state to macroscale solid state. Under ultraviolet light irradiation, SPD in solution can exhibit distinct color changes due to the photoisomerization from closed-ring (SPDC) isomer to open-ring (SPDO) isomer. Meanwhile, the assembly morphology can be dramatically transformed from nanospheres into rod-like structures. Density functional theory calculations demonstrate that SPDO assemblies have richer van der Waals forces than SPDC assemblies, which may induce morphological transformation. Furthermore, SPD can exhibit efficient and reversible photochromism and fluorescence switching in the solid state because the twisted TPE group can induce loose molecular stacking and provide significant free volumes for photoisomerization. Taking advantage of the efficient and reversible photochromic behaviors, we have successfully demonstrated that SPD is an excellent material for rewritable optical printing and a multi-level anti-counterfeiting material for dynamic information encryption.