Dependence of Photoinduced Bending Behavior of Diarylethene Crystals on Ultraviolet Irradiation Power

The photoinduced bending behavior of diarylethene crystals upon irradiation with various ultraviolet (UV) light intensities was investigated. The bending velocity of the photoinduced bending crystals was estimated from the curvature of the bending crystal. The initial velocity of curvature change (V-init) increased in proportion to the power of the incident UV light even when the crystal thickness was different, which suggests that the local strain caused by photo-isomerization makes a cumulative contribution to the bending behavior. Moreover, for all UV light intensities, the relationship between V-init, and the crystal thickness was well explained by the easily handled Timoshenko bimetal model. This result provides a validated method for the quantitative evaluation of the photoinduced bending velocity in various molecular crystals.