Biaxial smectic A phase in homologous series of compounds composed of highly polar unsymmetrically substituted bent-core molecules
作者:B. K. Sadashiva、R. Amaranatha Reddy、R. Pratibha、N. V. Madhusudana
DOI:10.1039/b109546c
日期:2002.3.21
Several compounds belonging to three new series of five-ring banana-shaped esters, which are unsymmetrically substituted with respect to the central phenyl ring, have been synthesised. One of the arms of these bent-core molecules has been terminally substituted with a highly polar cyano group while the other end contains an alkoxy chain. The mesophases exhibited by these compounds have been characterised using a combination of optical polarising microscopy, differential scanning calorimetry and X-ray diffraction studies. These studies indicate that most of the compounds show two smectic A mesophases which have a partial bilayer ordering. Conoscopic experiments clearly reveal that the lower temperature smectic A phase is biaxial in nature. A structural model has been proposed for the lower temperature biaxial smectic A phase. It is argued that quartets of molecules, which are conducive to the formation of the biaxial phase, can form in the layers. The in-layer birefringence of
the biaxial smectic A phase has also been measured as a function of temperature for one of the compounds.
我们合成了属于三个新的五环香蕉形酯系列的几种化合物,这些化合物的中心苯基环被非对称取代。这些弯曲核心分子的一个臂末端被高极性氰基取代,而另一端则含有烷氧基链。通过结合使用光学偏振显微镜、差示扫描量热法和 X 射线衍射研究,对这些化合物的介相进行了表征。这些研究表明,大多数化合物显示出两种具有部分双层有序性的 A 介相。显微镜实验清楚地表明,温度较低的共晶 A 相具有双轴性质。为低温双轴共晶 A 相提出了一个结构模型。该模型认为,有利于形成双轴相的分子四元组可以在层中形成。还测量了其中一种化合物的双轴共晶 A 相的层内双折射随温度变化的情况。