The Synthesis and Evaluation of Novel Bent-core Liquid Crystals Designed to Generate a Biaxial Nematic Phase

人们普遍认为物质可以以三种状态存在：固体、液体和气体，然而，一些材料，特别是那些由棒状分子组成的材料，可以额外显示一个或多个“液晶”相。液晶相是物质的不同相，其分子顺序介于普通液态和普通结晶固态之间。近晶相（有几种是已知的）是非常粘稠的液体，因为分子的有序程度接近固体。向列相是非常流动的，因为唯一的分子顺序是分子的统计平行排列。正是这种流体向列状液晶被广泛用于平板液晶显示器，现在用于手表、计算器、移动电话、相机、笔记本电脑、台式显示器和最近的大面积平板电视。在这些器件中，棒状液晶分子通过施加一个小电场（几伏特）来切换它们的方向，虽然切换时间相当快，大约50微秒，更快的切换将是有利的，并在显示，电信和光学器件中开辟了一个全新的快速切换应用领域。在向列相中，棒状分子具有统计上平行的分子排列，并且在这种排列中只有一个轴（光轴），偏振光通过该轴以等速度传播，因此称为单轴相。弯核（但不是太弯曲）分子也可以表现出向列相，然而，弯核分子结构可以产生双轴向列相，顾名思义，其中有两个光轴。双轴向列相具有基本的科学意义，此外，它还具有技术意义，因为在这样的双轴向列相中切换将更快地实现上述优势器件，并可能促进新型高科技应用的发展。到目前为止，很少有化合物被证明能产生双轴向列相，而且这些化合物只在200℃左右的温度下，在相对较短的温度范围内表现出来；这显然使评估变得困难，并且不可能在应用中使用。本研究旨在通过新材料设计的合成和评估，深入研究双轴向列相生成过程中弯核分子结构的结构-性能关系，以期在更宽的温度范围内，在室温或接近室温的条件下提供相；从而促进了物理性质的评估并使其能够在上述应用中使用。

It is commonly recognised that matter can exist in three states, solid, liquid and gas, however, some materials, notably those that consist of rod-shaped molecules, can additionally show one or more 'liquid crystal' phase(s). Liquid crystal phases are distinct phases of matter that have molecular orderings intermediate between those of the common liquid state and those of the common crystalline solid state. The smectic phases (several are known) are liquids that are quite viscous because the degree of molecular ordering is close that of solids. The nematic phase is very fluid because the only molecular ordering is a statistically parallel arrangement of molecules. It is this fluid nematic liquid crystal that is used in the widely available flat-panel liquid crystal displays that are now used for watches, calculators, mobile telephones, cameras, lap-top computers, desk-top monitors and more recently large area flat-panel televisions. In these devices, the rod-like liquid crystal molecules have their orientation switched by the application of a small electric field (a few volts), and although switching times are quite fast, around 50 microseconds, faster switching would be advantageous, and open up a whole new area of fast switching applications in displays, telecommunications and optical devices.In the nematic phase, the rod-like molecules have a statistically parallel arrangement of the molecules and in this arrangement there is only one axis (the optic axis) through which polarised light travels through with equal velocity, hence the phase is termed uniaxial. Bent-core (but not too bent) molecules can also exhibit the nematic liquid crystal phase, however, the bent-core molecular structure can give rise to a biaxial nematic phase, in which, as the name implies, there are two optic axes. A biaxial nematic phase is of fundamental scientific interest, and additionally it is of technological interest because switching in such a biaxial nematic phase would be much faster enabling the advantageous devices mentioned above, and possibly facilitate the development of novel high technology applications.So far, very few compounds have been proven to generate a biaxial nematic phase, and these are only exhibited at temperatures of around 200 C, and over a relatively short temperature range; which obviously makes evaluation difficult, and use in applications impossible. This proposed research is designed to thoroughly investigate the structure-property relationships of bent-core molecular structures in the generation of the biaxial nematic phase, through the synthesis and evaluation of novel material designs, with a view to providing the phase over a wider temperature range, at or close to room temperature; thus facilitating the evaluation of physical properties and enabling use in applications discussed above.