Cyclic Photothermal‐Actuated Organic Crystals for Reconfigurable Optical Waveguides

ABSTRACT Photomechanically responsive crystals are emerging as intelligent materials for micro/nano manipulation, biomimetic machines, and adaptive systems. However, their practical deployment is often hindered by limited reversibility and fatigue resistance. Herein, we report an acylhydrazone‐based organic compound that forms elastic crystals capable of UV‐triggered E to Z photoisomerization, inducing backlight photomechanical bending. The bent crystals fully recover to the straight state upon heating, where thermal energy releases the accumulated internal stress and enables structural restoration. Notably, the crystals preserve rapid bending and recovery behavior over 500 bending–recovery cycles, while maintaining fluorescence performance and retaining intact surface and internal structures, indicating excellent fatigue resistance. Moreover, the bending angle can be precisely controlled by UV irradiation, enabling reconfigurable passive optical waveguides. These findings open broad prospects for flexible electronics, light‐driven microdevices, and next‐generation information technologies.