Photomechanical bending behavior of photochromic diarylethene crystals induced under polarized light

Materials that change their shape by external stimuli have been attracting much attention as artificial mesoscopic actuators. In particular, photoresponsive molecular crystals are promising materials as photoactuators. Although many kinds of crystals exhibiting photomechanical motions have been reported so far, in many cases, light is irradiated to the crystal homogeneously. The details of the effect of irradiation conditions have not been specifically examined. Herein, the effect of polarized ultraviolet (UV) light on the photomechanical bending motion of diarylethene crystals was investigated. The bending speed upon polarized UV light irradiation depended on the polarization angle. The dependence of the bending speed was well correlated with the absorption anisotropy of the open-ring isomer in the crystal, which indicates that the photochromic reaction depth from the crystal surface played an important role in controlling the bending speed.