Integrating dual photoresponsive molecules via a cocrystal strategy: photosalient effects, negative photochromism, and fluorescence enhancement

Integrating multiresponsive molecules into a single crystal is a novel attempt in the area of photomechanical crystalline materials. In this work, a photomechanical crystal (9AC-NPE; 9AC = 9-anthracenecarboxylic acid, NPE = 4-(1-naphthylvinyl) pyridine) was prepared via cocrystallization. Remarkably, this cocrystal contained two distinct photoresponsive molecules, each corresponding to undergo a unique photodimerization reaction. Although these molecules need to satisfy appropriate topological stacking criteria, both photodimerization reactions occurred under ultraviolet irradiation, contributing to the photosalient effects, negative photochromism, and fluorescence enhancement of the cocrystal. The photosalient behavior of the cocrystal under white-light irradiation prompted us to further examine the differences between the two photodimerization reactions, particularly their reaction rate and response wavelength. Furthermore, the utility of this system in optical printing was demonstrated. Therefore, this work enhances the understanding of the design and application of photomechanical crystalline materials and can serve as an important reference for future efforts in this field.