Induction and modulation of chirality in smectic 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产生快速开关开关，用于高分辨率显示应用。为了获得无缺陷的FLC薄膜，SmC*液晶混合物需要具有最少量的手性材料。为了满足这一重要要求，本研究的重点是在近晶相中诱导手性，以及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Ps值。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。本研究的第二个方面侧重于设计手性分子，这些手性分子可以通过氢键自组装，从而在SmC*相中形成具有增强非线性光学性质的极性网络。本研究的第三个方面是设计手性掺杂剂，使其在光照射下发生可逆的结构变化，而不发生热反反应或降解。在SmC主机中，光诱导的结构变化旨在以触发FLC光快门的ON-OFF开关的方式调制诱导Ps的大小，从而使FLC薄膜中的图像、衍射光栅和波导能够写入。

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 ON-OFF light shutter that is used in high-resolution display applications.  In order to obtain defect-free FLC films, SmC* liquid crystal mixtures with a minimum amount of chiral material are required.  To address this important requirement, the proposed research focuses on the INDUCTION of chirality in smectic phases, and how a chiral dopant can propagate its handedness most effectively in a non-chiral SmC host to produce increasingly large Ps values.  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 the proposed research focuses on the design of chiral molecules that can self-assemble via hydrogen bonding to give a polar network in the SmC* phase with enhanced non-linear optical properties.  A third aspect of the proposed research is the design of chiral dopants that undergo a reversible structural change upon irradiation with light without thermal back reaction or degradation.  In a SmC host, the light-induced structural change is intended to MODULATE the magnitude of induced Ps in such a way as to trigger the ON-OFF switching of a FLC light shutter, which would enable the writing of images, diffraction gratings and waveguides in FLC films.