Parisi Emmanuele, Santagata Emanuela, Kula Przemysław, Herman Jakub, Gupta Sakuntala, Simone Elena, Zarrella Salvatore, Korter Timothy M, Centore Roberto
Department of Applied Science and Technology, Politecnico of Turin, I-10129 Turin, Italy.
Department of Chemical Sciences, University of Naples Federico II, Via Cintia, I-80126 Naples, Italy.
J Am Chem Soc. 2025 Apr 30;147(17):14731-14738. doi: 10.1021/jacs.5c03448. Epub 2025 Apr 17.
Thermosalient transitions are a subset of single-crystal-to-single-crystal (SCSC) transitions, in which the change of lattice parameters is highly anisotropic and very fast. As a result, crystals at the transition undergo macroscopic dynamical effects (hopping, jumping, and shattering). These transitions feature a conversion of heat to mechanical energy that can be exploited in the realization of advanced materials. Most thermosalient transitions are observed at temperatures higher than room temperature. Examples of low-temperature thermosalient transitions are rare. We describe a new example of a low-temperature thermosalient transition in a sexiphenyl compound. At about -40 °C, the parent single crystal (phase I) shatters into single crystal fragments of the new phase (phase II). The two phases have been studied by single-crystal X-ray analysis using a synchrotron source, variable-temperature Raman spectroscopy, and computational analysis of lattice normal vibration modes. A mechanism of the transition is proposed. We confirm colossal thermal expansion coefficients and supercells as reliable features of thermosalient transitions and add as a third feature a low-frequency principal optical vibration of the crystal lattice prompting the transition. Based on this, a roadmap for the automated prediction of thermosalient transitions in molecular crystals is also outlined.
热致跃变是单晶到单晶(SCSC)转变的一个子集,其中晶格参数的变化具有高度各向异性且非常迅速。因此,处于转变过程中的晶体经历宏观动力学效应(跳跃、跳动和破碎)。这些转变的特点是热向机械能的转化,可用于实现先进材料。大多数热致跃变在高于室温的温度下观察到。低温热致跃变的例子很少。我们描述了一种六苯基化合物中低温热致跃变的新例子。在约 -40 °C时,母单晶(相I)破碎成新相(相II)的单晶碎片。通过使用同步辐射源的单晶X射线分析、变温拉曼光谱以及晶格法向振动模式的计算分析对这两个相进行了研究。提出了一种转变机制。我们确认巨大的热膨胀系数和超晶胞是热致跃变的可靠特征,并将促使转变的晶格低频主光学振动作为第三个特征补充进来。基于此,还概述了分子晶体中热致跃变自动预测的路线图。