Abrupt and Reversible Stretching in an Azobenzene Single Crystal via Thermal Phase Transition.

Mechanically responsive crystals are promising for actuators and microrobotics; however, achieving large reversible deformation with high durability remains challenging. Herein, A single-component azobenzene crystal is reported to exhibit an abrupt and reversible stretching of over 8% along its long axis, driven by a thermally induced single-crystal-to-single-crystal phase transition. Single-crystal X-ray diffraction revealed a significant change in molecular packing distance along the long axis accompanied by the reorientation of CH-π interactions, leading to large macroscopic stretching/shrinking. Furthermore, visible light (435 nm) induced rapid, localized, and reversible stretching of the crystal via the photothermal effect, enabling the remote control of microparticle motion. This study reveals a rare combination of large anisotropic deformation, reversibility, and light responsiveness in a single-component organic crystal, offering a new molecular platform for advancing micro-energy conversion and soft robotics.