Substituent-Engineered Multi-Stimuli-Responsive Schiff Base Crystals: from Proton Transfer Mechanisms to Smart Device Prototypes

The demand for multifunctional, stimuli-responsive crystalline materials capable of stable, rapid, and diverse responses is critical for smart sensing, actuation, and optoelectronics, yet remains challenging in single-component systems. Using substituent replacement in crystal engineering, we modulated crystal packing density to balance ESIPT efficiency, yielding three Schiff base derivatives. In this study, compound B manifests concurrent photochromism and intrinsic elastoplasticity, demonstrating dual photoresponsive behavior. Compound C exhibits robust thermochromism coupled with spontaneous crystal jumping at elevated temperatures. Compound Bu-C displays thermochromism with high-temperature fluorescence quenching while undergoing exceptional, phototriggered explosive decomposition. We establish structure–property relationships linking molecular design to photochromism, thermochromism, mechanoresponse, and photothermal sensing. Mechanistic studies confirm proton-transfer tautomerism underpins photo/thermochromism, while lattice stress release enables mechanoresponse. Leveraging the crystal’s thermochromism, photochromism, and temperature-dependent fluorescence, we demonstrate a photoregulated thermal switch and a multistage anticounterfeiting technology. This work provides novel design principles for advanced multiresponsive crystals, significantly expanding their potential in actuators, sensors, and optoelectronic systems beyond single-function materials.