Crystals of charge-transfer (CT) complexes were synthesized using the polar molecule tetrachlorophthalonitrile (TCPN) as the electron acceptor and nonpolar aromatic hydrocarbons, such as perylene, coronene, chrysene, and pyrene, as the electron donors. Variable-temperature X-ray crystal structure analyses revealed that the TCPN molecules in all the CT crystals exhibit orientational disorder at room temperature. Some of the CT crystals undergo an order–disorder-type phase transition upon cooling, where the orientation of the TCPN molecules becomes ordered at low temperature. The CT crystals show large dielectric constants at room temperature arising from in-plane reorientation of the polar TCPN molecules. The order–disorder phase transition results in a drastic reduction of the dielectric constant of the CT crystals upon cooling. This study demonstrates that the formation of CT crystals from polar molecules represents a promising method for the development of dielectric crystalline materials, whose properties vary significantly in response to phase transitions.

中文翻译：

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带有极性分子重定向的电荷转移配合物晶体：介电性质和有序无序相变

使用极性分子四氯邻苯二甲腈（TCPN）作为电子受体，使用非极性芳族烃（例如per，co 、,和，）作为电子供体，合成了电荷转移（CT）络合物的晶体。可变温度X射线晶体结构分析表明，所有CT晶体中的TCPN分子在室温下均表现出取向紊乱。一些CT晶体在冷却时会经历有序-无序类型的相变，其中TCPN分子的取向在低温下变得有序。CT晶体在室温下显示出大的介电常数，这是由于极性TCPN分子的面内重新取向而引起的。有序-无序相变导致冷却时CT晶体的介电​​常数急剧降低。