Turning on Photomechanical Responses in Molecular Crystals of Anthracenyl Thiazole Derivatives by Regulating Intermolecular Interactions

Photomechanical molecular crystals driven by solid-state photochemical reactions can exhibit various mechanical motions when exposed to light, showing promising potential applications in intelligent materials and devices in the future. A rational molecular structure design is necessary to realize versatile photoresponsive motions in different crystals. Herein, we synthesized two new molecular crystals: (E)-2-(2-(anthracen-9-yl)vinyl)thiazole ((E)-AT) and (E)-3-(anthracen-9-yl)-2-(thiazol-2-yl)acrylonitrile ((E)-ATCN), and four similar reference molecules (R1, R1-CN, R2, and R2-CN) composed of the anthracene or naphthalene framework and a thiazole or benzothiazole unit. The molecules of (E)-ATCN solids could undergo an E-to-Z photoisomerization reaction, and the corresponding crystalline microribbons showed vigorous photomechanical responses, including bending, twisting, elongation, and curling upon visible light irradiation. Besides, the photomechanical movements of the (E)-ATCN microribbons could be switched off by adding an acidic solution, and photomechanical motions could be reobserved if a base solution neutralized the acid. Nevertheless, (E)-AT, which possessed a similar molecular structure to (E)-ATCN, underwent reversible photoisomerization in solutions while being photoinert in the solid state. Through comparison with reference molecules, both experimental measurements and computational calculations showed that the electron-withdrawing cyano group (−CN) at the vinyl structure of the (E)-ATCN molecule had a significant influence on the crystal packing structure and intermolecular interactions, which favored the photomechanical motions and solid-state photochemistry in the (E)-ATCN crystals. Our results showed a facile way to use functional groups, such as an electron-withdrawing unit, to regulate intermolecular interactions and crystal structures to realize photomechanical responses in molecular crystals.