Visible-Light-Driven Deformation Triggered by [2 + 2] Cycloaddition Reactions within Isostructural Molecular Crystals

Photoresponsive molecular crystals with superior precise control and remote operation are considered the preferred candidates for smart materials. However, conventional photoresponsive crystals typically require high-energy and biologically damaging ultraviolet light for activation. Herein, we report three visible-light-responsive isostructural molecular crystals of cyano-styrene derivatives (DOPA-F, DOPA-Cl, and DOPA-Br) based on the [2 + 2] cycloaddition reaction. These crystals exhibit unique reactivities and macroscopically dynamic behaviors, attributed to distinct reaction pathways resulting from subtle differences in the hierarchical structure of the π-dimers. Here, the π-dimer refers to the interacting molecular pairs involved in photodimerization. Specifically, DOPA-F crystals exhibit rapid helical twisting and bending under irradiation, while DOPA-Cl and DOPA-Br bend away from the light. Moreover, DOPA-F undergoes a structural reorganization from one crystalline state to another, in contrast to DOPA-Cl and DOPA-Br, which transform from a crystalline state to an amorphous form. This work constructs eco-friendly photoresponsive materials and highlights the significant impact of subtle variations in hierarchical architecture on controlling reaction dynamics, pathways, and macroscopically dynamic behaviors.