National Engineering Research Centre of Industrial Crystallization Technology, School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, P. R. China.
Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore, 117585, Singapore.
Chemistry. 2023 Jan 2;29(1):e202202598. doi: 10.1002/chem.202202598. Epub 2022 Nov 14.
Multiple stimuli-responsive molecular crystals are attracting extensive attentions due to their potential as smart materials, such as molecular machines, actuators, and sensors. However, the task of giving a single crystal multiple stimuli-responsive properties remains extremely challenging. Herein, we found two polymorphs (Form O and Form R) of a Schiff base compound, which could respond to multiple stimuli (external force, acid, heat). Form O and Form R have different elastic deformability, which can be attributed to the differences in the molecular conformation, structural packing and intermolecular interactions. Moreover, both polymorphs exhibit reversible bending driven by volatile acid vapor, which we hypothesize is caused by reversible protonation reaction of imines with formic acid. In addition, jumping can be triggered by heating due to the significant anisotropic expansion. The integration of reversible bending and jumping into one single crystal expands the application scope of stimuli-responsive crystalline materials.
多种刺激响应的分子晶体由于其在智能材料（如分子机器、致动器和传感器）中的潜在应用而受到广泛关注。然而，赋予单晶多种刺激响应性质的任务仍然极具挑战性。在这里，我们发现了一种席夫碱化合物的两种多晶型物（O 型和 R 型），它们可以对外力、酸、热等多种刺激做出响应。O 型和 R 型具有不同的弹性变形能力，这可以归因于分子构象、结构堆积和分子间相互作用的差异。此外，两种多晶型物都表现出由挥发性酸蒸气驱动的可逆弯曲，我们假设这是由于亚胺与甲酸之间的可逆质子化反应引起的。此外，由于各向异性膨胀显著，加热可以引发跳跃。将可逆弯曲和跳跃集成到单个单晶中，扩展了刺激响应晶体材料的应用范围。
