Rational Design of ferroelectric liquid crystals

手性是许多天然和人造物质以及几乎所有生物都具有的独特性质。手性物体以右手和左手形式存在（对映体），例如手套、鞋子和高尔夫球杆，并且在其镜像上是不可重叠的。手性在分子尺度上也表现出来。例如，氨基酸、碳水化合物和许多其他天然产物。这些手性构件通过共价和非共价相互作用组装，形成更大的手性结构，如蛋白质和核酸，它们自己组装成具有手性拓扑结构的晶体结构。这种宏观水平的分子手性表现，最早是由巴斯德1848年用酒石酸铵钠发现的，在手性近晶C* (SmC*)液晶相中也以铁电极化（Ps）的形式被观察到。铁电液晶（FLC）的极化可以耦合到电场中，以产生可用于高分辨率显示应用的快速开关光快门。为了生产适合显示的FLC薄膜，SmC*液晶混合物与最少量的手性材料是必需的。为了解决这一重要要求，我们的研究计划集中在近晶相中手性的诱导，以及轴向手性掺杂剂如何在非手性SmC宿主中最有效地传播其手性以产生越来越大的极化功率。这可以通过匹配手性掺杂剂和SmC宿主的分子结构来实现，从而通过分子间相互作用最大化手性转移。该计划的第二个方面侧重于SmC液晶的合理设计，这些液晶经历了从非倾斜的近晶A （SmA）相到倾斜的SmC相的最小层收缩。我们的分子设计策略是基于实现两个结构元素之间的“挫折”，从而促进SmA和SmC相的形成。这些所谓的“类de vries”材料将解决FLC技术在LCD投影仪和大型平板显示器中使用的主要障碍之一：FLC混合物从手性SmA*冷却到SmC*相时，由于层收缩而形成之形缺陷。

Chirality is a unique property that many natural and man-made substances and almost all living things possess. Chiral objects exist in right- and left-handed forms (enantiomers), e.g., gloves, shoes and golf clubs, and are non-superposable on their mirror images. Chirality is also manifest at the molecular scale., e.g., amino acids, carbohydrates, and many other natural products. These chiral building blocks assemble via covalent and non-covalent interactions to form larger chiral structures such as proteins and nucleic acids, which themselves assemble into crystalline structures with chiral topographies. Such manifestation of molecular chirality at the macroscopic level, which was first shown by Pasteur in 1848 with sodium ammonium tartrate, is also observed in the chiral smectic C* (SmC*) liquid crystal phase in the form of a ferroelectric polarization (Ps). The polarization of a ferroelectric liquid crystal (FLC) can be coupled to an electric field to produce a fast switching light shutter that can be used in high-resolution display applications. In order to produce FLC films suitable for displays, SmC* liquid crystal mixtures with a minimum amount of chiral material are required. To address this important requirement, our research program focuses on the induction of chirality in smectic phases, and how an axially chiral dopant can propagate its handedness most effectively in a non-chiral SmC host to produce increasingly large polarization powers. This can be achieved by matching the molecular structures of chiral dopants and SmC hosts to maximize chirality transfer via intermolecular interactions. A second aspect of this program focuses on the rational design of SmC liquid crystals that undergo a transition from the non-tilted smectic A (SmA) phase to the tilted SmC phase with minimal layer contraction. Our molecular design strategy is based on achieving a 'frustration' between two structural elements that promote the formation of SmA and SmC phases. These so-called 'de Vries-like' materials will provide a solution to one of the main roadblocks to the use of FLC technology in LCD projectors and large flat panel displays: the formation of zigzag defects caused by layer contraction upon cooling a FLC mixture from the chiral SmA* to the SmC* phase.