Ordered Matter Science Research Center, Southeast University, Nanjing 211189, China.
J Am Chem Soc. 2011 Aug 17;133(32):12780-6. doi: 10.1021/ja204540g. Epub 2011 Jul 25.
Molecular motion is one of the structural foundations for the development of functional molecular materials such as artificial motors and molecular ferroelectrics. Herein, we show that pendulum-like motion of the terminal group of a molecule causes a ferroelectric phase transition. Complex 4-methoxyanilinium tetrafluoroborate-18-crown-6 (C(7)H(10)NO(18-crown-6)BF(4), 1) shows a second-order ferroelectric phase transition at 127 K, together with an abrupt dielectric anomaly, Debye-type relaxation behavior, and the symmetry breaking confirmed by temperature dependence of second harmonic generation effect. The origin of the polarization is due to the order-disorder transition of the pendulum-like motions of the terminal para-methyl group of the 4-methoxyanilinium guest cation; that is, the freezing of pendulum motion at low temperature forces significant orientational motions of the guest molecules and thus induces the formation of the ferroelectric phase. The supramolecular bola-like ferroelectric is distinct from the precedent ferroelectrics and will open a new avenue for the design of polar functional materials.
分子运动是人工马达和分子铁电体等功能分子材料发展的结构基础之一。本文中，我们展示了分子末端基团的钟摆运动导致铁电相转变。化合物 4-甲氧基苯胺四氟硼酸盐-18-冠-6([C(7)H(10)NO(18-冠-6)]+[BF4]-，1)在 127 K 时表现出二级铁电相转变，同时伴有介电异常、德拜型弛豫行为以及通过二次谐波产生效应的温度依赖性证实的对称破缺。极化的起源归因于 4-甲氧基苯胺客体阳离子末端对甲基基团的钟摆运动的无序-有序转变；也就是说，低温下钟摆运动的冻结迫使客体分子进行显著的取向运动，从而诱导铁电相的形成。超分子球棒型铁电体与先前的铁电体不同，将为设计极性功能材料开辟新途径。
