Quadruple Stimuli-Responsive Behaviour of Acylhydrazone Crystals: Mechanical, Photomechanical, Thermomechanical, and Optical Waveguide Properties.

As society advances, the demand for high-performance crystal materials with versatile stimuli-responsive capabilities has increased. However, there remains a notable shortage of simple molecular crystals that exhibit stable and swift responses to various stimuli. In this study, we synthesized a novel acylhydrazone crystal by integrating benzene-fused heterocycles and halogens, achieving a crystal material with multiple stimuli-responsive behaviours. The crystal demonstrates good mechanical flexibility, capable of with standing a strain of 2.3 % under applying mechanical force and recovering its original shape after force removal. Crystal structure analysis reveals this property is due to the strong and flexible intermolecular interactions. It also exhibits rapid photomechanical bending away from light source under UV irradiation, which could be attributed to the facile photoisomerization. Moreover, the crystal undergoes significant thermomechanical transitions, including cracking and jumping, upon heating. Additionally, the prepared crystal exhibits passive optical waveguide of red light at 640 nm, which, combining the photomechanical bending, can achieve controllable light output direction. These multi-stimuli-responsive behaviors make the acylhydrazone crystal a promising candidate for applications in multifunctional sensors, optoelectronic devices, and thermal switches. This work provides a helpful reference for the study of potential crystal material design and functionality of advanced responsive systems.