Crystal thickness dependence of the photoinduced crystal bending of 1-(5-methyl-2-(4-(p-vinylbenzoyloxymethyl)phenyl)-4-thiazolyl)-2-(5-methyl-2-phenyl-4-thiazolyl)perfluorocyclopentene

Abstract

Rod-like crystals of 1-(5-methyl-2-(4-(p-vinylbenzoyloxymethyl)phenyl)-4-thiazolyl)-2-(5-methyl-2-phenyl-4-thiazolyl)perfluorocyclopentene with lengths of over 1 mm showed photoreversible bending over 100 cycles upon irradiation with alternating ultraviolet (UV) and visible light. The crystals bent toward the incident light due to a contraction of the crystal length and a gradient of the crystal thickness, which depend on the extent of photoisomerization. It was observed that the bending speed depends on the crystal thickness, and the curvature change on changing the crystal thickness agrees well with Timoshenko's bimetal model, as well as with the observation that crystals of 1,2-bis(2-methyl-5-(4-(1-naphthoyloxymethyl)phenyl)-3-thienyl)perfluorocyclopentene bend away from the incident light due to an expansion of the crystal length and a gradient of the crystal thickness, which depend on the extent of photoisomerization. It was revealed that Timoshenko's bimetal model can be applied to photoinduced crystal bending behaviors caused by both contraction and expansion. These findings are very useful for evaluating and designing photomechanical actuators.