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

Crystals of azobenzene compounds exhibit abrupt and reversible stretching and shrinking in response to thermal and photo stimulation. The single‐crystal‐to‐single‐crystal phase transition between two polymorphs involving reorientation of CH–π hydrogen interactions are demonstrated. Furthermore, the abrupt photoinduced stretching of the crystals is used to trigger microparticle transportation. Abstract 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. Crystals of azobenzene compounds exhibit abrupt and reversible stretching and shrinking in response to thermal and photo stimulation. The single-crystal-to-single-crystal phase transition between two polymorphs involving reorientation of CH–π hydrogen interactions are demonstrated. Furthermore, the abrupt photoinduced stretching of the crystals is used to trigger microparticle transportation. Abstract 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. Advanced Science, Volume 12, Issue 48, December 29, 2025.