Turning on Photomechanical Responses in Molecular Crystals of Anthracenyl Thiazole Derivatives by Regulating Intermolecular Interactions
Chenchen Zhang, Tianle Zhang, Tianyuan Li, Tian‐Yi Xu, Fei Tong
Abstract
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.