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

Abstract

Photomechanical molecular crystals driven by solidstate 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 solidstate photochemistry in the (E)-ATCN crystals. Our results showed a facile way to use functional groups, such as an electronwithdrawing unit, to regulate intermolecular interactions and crystal structures to realize photomechanical responses in molecular crystals.

Superelastic and Photomechanical Behavior of Acylhydrazone Derivative Crystals

“…Stimuli-responsive molecular crystals hold vast potential across various fields, including artificial muscles, microrobots, optical switches, and oscillators, and attract considerable attention from materials scientists. When subjected to stimuli such as humidity, heat, mechanical force, light, and magnetic fields, these crystals demonstrate remarkable mechanical responses, including bending, stretching, twisting, curling, plasticity, and elastic bending. − Light, as a stimulus, offers advantages such as noncontact operation and precise control with remote accessibility. As early as 1834, Trommsdorff reported the “explosive” phenomenon observed in α-santonin crystals under sunlight irradiation .…”