Induction and modulation of chirality in smectic liquid crystals

手征性是许多天然和人造物质以及几乎所有生物都具有的一种独特性质。 手性对象以右手和左手形式（对映异构体）存在，例如，手套、鞋和高尔夫球杆，并且在它们的镜像上是不可重叠的。 手性在分子尺度上也很明显。例如，在一个实施例中，氨基酸、碳水化合物和许多其他天然产物。这些手性结构单元通过共价和非共价相互作用组装以形成较大的手性结构，例如蛋白质和核酸，其本身组装成具有手性形貌的晶体结构。 这种分子手性在宏观水平上的表现，首先由巴斯德在1848年用酒石酸铵钠显示，也以铁电极化（Ps）的形式在手性近晶C*（SmC*）液晶相中观察到。 铁电液晶（FLC）的极化可以耦合到电场以产生用于高分辨率显示应用中的快速切换开-关光快门。 为了获得无缺陷的FLC膜，SmC* 液晶混合物与最小量的手性材料是必需的。 为了解决这个重要的要求，拟议的研究集中在近晶相的手性诱导，以及如何手性掺杂剂可以传播其手性最有效地在非手性SmC主机产生越来越大的Ps值。 这可以通过匹配手性掺杂剂和SmC主体的分子结构来实现，以通过分子间相互作用最大化手性转移。 所提出的研究的第二个方面集中在手性分子的设计上，所述手性分子可以通过氢键自组装以在SmC* 相中提供具有增强的非线性光学性质的极性网络。 所提出的研究的第三个方面是手性掺杂剂的设计，其在用光照射时经历可逆的结构变化而没有热逆反应或降解。 在SmC主体中，光诱导的结构变化旨在以触发FLC光快门的开-关切换的方式调制诱导的Ps的幅度，这将使得能够在FLC膜中写入图像、衍射光栅和波导。

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.