Broad-Wavelength Light-Fuelled Organic Crystal Oscillators Driven by Multimodal Photothermally Resonated Natural Vibration

Photomechanical crystals have applications in light-fuelled actuators and soft robots. Herein, we describe light-responsive, versatile, anthraquinone dye crystal oscillators actuated via natural vibrations that are resonated by a photothermal effect. A black needle-shaped crystal cantilever oscillates at 70 Hz in the first mode of natural vibration upon irradiation by broad-wavelength light ranging from the ultraviolet through the visible to the near infrared, and also under continuous-wavelength light (400–2000 nm). The second and third natural vibration modes are induced at higher frequencies (530 and 1350 Hz) and evidence complex flagellum-like motions. The frequency can be readily tuned by moving the support of a crystal piece; this is analogous to playing a guitar. The crystal exhibits high durability (more than 10,000 cycles): the high elasticity prevents deterioration. Oscillatory motions can be designed via simulations using finite element analysis. This work will facilitate the use of photomechanical crystals in light-fuelled soft robots.