Photoinduced Multistep Bending of 7‑Acetoxy-4-methylcoumarin Crystal

Photomechanical materials driven by external optical stimuli can be remotely operated without contact. Photoinduced bending, one of the typical photomechanical operations, is a promising action for actuator materials. For the control of complicated operations, it is important to construct a system that can work with multistep bending. Here, we report photoinduced multistep bending using rod-shaped crystals of 7-acetoxy-4-methylcoumarin. Upon 365 nm UV light irradiation to the crystals, they displayed up to three-step bending: expansion due to the repulsion between the unreacted material and the photoproduct, shrinkage due to the subsequent increase in the photoproduct, and expansion due to the amorphization caused by photodimerization. The number of bending steps depended on the thickness of the crystals: three steps with a thickness of 25 μm or greater and two steps with a thickness of 22 μm or less.