Rational Design of Smectic Liquid Crystals for Electro-Optical Applications

手性是人造和几乎所有生物都具有的特性。手性物体以右手和左手的形式存在（例如手套、高尔夫球杆），并且在它们的镜像上是不重叠的。手性在分子尺度上也表现出来。（如氨基酸、碳水化合物）；这些手性构建块通过自然组装形成更大的手性结构（例如，蛋白质，核酸），这些结构本身形成具有手性地形的晶体结构。这种宏观水平的分子手性表现，最早是由巴斯德在酒石酸铵钠晶体上发现的，通过形式手性和自发极化在层状（近晶）液晶相中得到揭示。例如，手性近晶C （SmC*）相具有螺旋结构，其分子倾斜方向沿层法线方向前进；它还表现出自发极化（PS），可以耦合到电场E产生用于高分辨率铁电液晶（FLC）微显示器的光电快门。非倾斜手性近晶A （SmA*）相表现出电斜效应（ECE），即分子在外加电场E的作用下发生倾斜；诱导倾斜角随E缩放，这使得显示器在时间尺度上产生灰度，比向列式lcd快几个数量级。PS和ECE都是手性体性质，分别取决于SmC*和SmA*相中手性组分的结构。我的研究项目侧重于理解分子结构与液晶相体性质之间的关系，作为合理设计铁电和电临床液晶混合物的手性和非手性（非手性）成分的基础。本研究的一个方面侧重于在近晶相中诱导手性，以及轴向手性分子如何在SmC*液晶相中通过分子间相互作用最有效地传播其手性以最大化自发极化。该计划的另一个方面侧重于液晶的合理设计，经历从非倾斜的SmA*相到倾斜的SmC*相的最小层收缩。这些所谓的“类de vries”材料为在投影仪和大型平板显示器中使用铁电液晶（FLC）技术的主要障碍之一提供了解决方案：在将FLC混合物从SmA*冷却到SmC*时，由于近晶层的屈曲而导致之形缺陷的形成。这些材料还具有明显的电诊所效应和最小的光学条纹缺陷，我们正在利用我们的设计专业知识开发新的SmA*液晶材料，这些材料在电诊所开关方面超过了目前的标准。

Chirality is a property that man-made and almost all living things possess. Chiral objects exist in right- and left-handed forms (e.g., gloves, golf clubs) and are non-superposable on their mirror images. Chirality is also manifest at the molecular scale. (e.g., amino acids, carbohydrates); these chiral building blocks are assembled by nature to form larger chiral structures (e.g., proteins, nucleic acids), which themselves form crystalline structures with chiral topographies. This manifestation of molecular chirality at the macroscopic level, which was first recognized by Pasteur with crystals of sodium ammonium tartrate, is revealed in lamellar (smectic) liquid crystal phases by form chirality and spontaneous polarization. For example, the chiral smectic C (SmC*) phase is characterized by a helical structure in which the molecular tilt orientation precesses about the layer normal; it also exhibits a spontaneous polarization (PS) that can be coupled to an electric field E to produce an electro-optical light shutter that is used in high-resolution ferroelectric liquid crystal (FLC) microdisplays. The non-tilted chiral smectic A (SmA*) phase exhibits an electroclinic effect (ECE) described by molecules tilting in response to an applied electric field E; the induced tilt angle scales with E, which enables the generation of a gray scale in displays on a time scale that is orders of magnitude faster than nematic LCDs. Both PS and ECE are chiral bulk properties that depend on the structure of the chiral constituent(s) in the SmC* and SmA* phases, respectively. My research program focuses on understanding the relationship between molecular structure and the bulk properties of liquid crystal phases as a foundation for the rational design of chiral and non-chiral (achiral) components of ferroelectric and electroclinic liquid crystal mixtures. One aspect of this research focuses on the induction of chirality in smectic phases, and how axially chiral molecules can propagate their handedness most effectively via intermolecular interactions in a SmC* liquid crystal phase in order to maximize the spontaneous polarization. Another aspect of this program focuses on the rational design of liquid crystals that undergo a transition from the non-tilted SmA* phase to the tilted SmC* phase with minimal layer contraction. These so-called 'de Vries-like' materials provide a solution to one of the main roadblocks to the use of ferroelectric liquid crystal (FLC) technology in projectors and large flat panel displays: the formation of zigzag defects caused by the buckling of smectic layers upon cooling a FLC mixture from the SmA* to the SmC* phase. These materials are also known to exhibit pronounced electroclinic effects with minimal optical stripe defects and we are leveraging our design expertise to develop new SmA* liquid crystal materials that exceed current standards in electroclinic switching.