Bending,Curling, Rolling,and Salient Behavior of Molecular Crystals Driven by [2+2] Cycloaddition of a Styrylbenzoxazole Derivative

We report interesting photomechanical behaviors of the dynamic molecular crystals of (E )‐2‐(2,4‐dichlorostyryl)benzod]oxazole ( BOACl24 ). The photosalient effect of the rod‐like crystal based on a metal‐free olefin driven by photodimerization is observed. Moreover, the needle‐like crystals of BOACl24 exhibit a reversible bending away from a UV light source. The nanofibers curl easily under UV irradiation in an organogel, in which the photo‐induced rolling of a small slice occurs. This suggests that the rapid release of the accumulated strain during photodimerization may lead to a photosalient effect, and the bending or curling happens when the strain is released slowly. Notably, 2+2] cycloaddition takes place between two different conformational isomers of BOACl24 on account of the rotation of the benzoxazole ring around the C?C bond in an excited state before photodimerization. Such topo‐photochemical reaction has not been reported elsewhere.