Department of Experimental Physics, Wrocław University of Science and Technology, Wybrzeże Stanisława Wyspiańskiego 27, 50-370 Wrocław, Poland.
Faculty of Science and Technology, Institute of Chemistry, University of Silesia in Katowice, 75 Pułku Piechoty 1A, 41-500 Chorzów, Poland.
Int J Mol Sci. 2022 May 6;23(9):5185. doi: 10.3390/ijms23095185.
Glass-forming ability is one of the most desired properties of organic compounds dedicated to optoelectronic applications. Therefore, finding general structure-property relationships and other rules governing vitrification and related near-glass-transition phenomena is a burning issue for numerous compound families, such as Schiff bases. Hence, we employ differential scanning calorimetry, broadband dielectric spectroscopy, X-ray diffraction and quantum density functional theory calculations to investigate near-glass-transition phenomena, as well as ambient- and high-pressure molecular dynamics for two structurally related Schiff bases belonging to the family of glycine imino esters. Firstly, the surprising great stability of the supercooled liquid phase is shown for these compounds, also under high-pressure conditions. Secondly, atypical self-organization via bifurcated hydrogen bonds into lasting centrosymmetric dimers is proven. Finally, by comparing the obtained results with the previous report, some general rules that govern ambient- and high-pressure molecular dynamics and near-glass transition phenomena are derived for the family of glycine imino esters. Particularly, we derive a mathematical formula to predict and tune their glass transition temperature () and its pressure coefficient (d/d). We also show that, surprisingly, despite the presence of intra- and intermolecular hydrogen bonds, van der Waals and dipole-dipole interactions are the main forces governing molecular dynamics and dielectric properties of glycine imino esters.
玻璃形成能力是专门用于光电应用的有机化合物最理想的特性之一。因此，找到控制玻璃化转变和相关近玻璃转变现象的一般结构-性质关系和其他规律，是许多化合物家族（如席夫碱）的当务之急。因此，我们采用差示扫描量热法、宽带介电谱、X 射线衍射和量子密度泛函理论计算来研究近玻璃转变现象，以及两种结构相关的席夫碱的环境和高压分子动力学，它们属于甘氨酸亚氨基酯家族。首先，对于这些化合物，即使在高压条件下，也显示出超冷液相惊人的高稳定性。其次，证明了通过分叉氢键进行非典型的自组织，形成持久的中心对称二聚体。最后，通过将获得的结果与以前的报告进行比较，为甘氨酸亚氨基酯家族推导出了一些控制环境和高压分子动力学以及近玻璃转变现象的一般规律。特别是，我们推导出了一个数学公式来预测和调整它们的玻璃化转变温度（Tg）及其压力系数（d/dT）。我们还表明，令人惊讶的是，尽管存在分子内和分子间氢键，但范德华力和偶极-偶极力是控制甘氨酸亚氨基酯的分子动力学和介电性质的主要力。
