The guest CH3CN molecule triggers solid-state photochromism in a Cu2I2-based MOF for advanced time-dependent encryption and inkless erasable printing

Abstract

It remains a big challenge to develop solid-state stimuli-responsive materials for time-dependent information encryption and inkless erasable printing with long retention times. Herein, a 2D Cu2I2-based MOF with photoresponsive spiropyran (SP) groups orderly installed on its skeleton is developed. The structural isomerization from SP to colored merocyanine (MC) form can be triggered by removing the CH3CN guests. Besides, the degree of structural isomerization and the retention time can be adjusted by controlling the amount of CH3CN guests, exhibiting dynamic photochromic behavior with multicolor states and tunable retention time. Based on these advantages, time-dependent information encryption is successfully achieved. Furthermore, the long retention time (>72 h) of the MC form under daylight conditions in the CH3CN-removed Cu2I2-based MOF and good repeatability make it promising in various applications, such as temporary calendars, price-cards, billboards, and reusable identity cards. This work provides a novel design strategy to fabricate multi-functional MOF-based smart materials for challenging applications of time-dependent information encryption and inkless erasable printing.