Liquid crystalline polymers with banana mesogens-Polarity and chirality induced by their banana shape

具有非线性分子形状的液晶化合物，即所谓的香蕉形分子，由于在这种非手性分子体系中发现了铁电性、反铁电性和色性，已成为液晶研究的一个富有成果的课题。通过对众所周知的香蕉形分子1,4-苯基[4-（4-n-烷氧基苯甲基）苯甲酸酯P-n-O-PIMB进行修饰，合成和研究了许多香蕉形液晶分子，随后揭示了各种液晶相和有趣的性质。本研究以2,5-二（4′-n-烷基羧基联苯基-4-基）-[1,3,4]-恶二唑（ODBBP-n）为核心，制备了一种新的香蕉形同源分子，扩展了对聚合物香蕉分子的研究。据我们所知，这是第一个表现出香蕉类中间相的五元杂环液晶分子。此外，还通过与噻唑类核心衍生物的比较，证明了ODBBP-n的弯曲几何形状与亚纯性之间的关系。得到的结果简单地描述如下。1)通过对B2相和B4相的手性记忆分析，认为自发产生手性是由于香蕉形状的手性构象特征。2)在铁电B2相中，由于自发极化和层弹性的相互作用，产生了明显的层波动。3)在具有不对称烷基尾部的香蕉分子中，当两个尾部基团的长度有显著差异时，反铁电相转变为铁电相。4)由于聚合物的高温熔融导致研究延伸到聚合物体系失败。现在，我们尝试合成香蕉分子的二聚体和三聚体。

Liquid crystalline compounds with non-linear molecular shape, so-called banana-shaped molecules, have become a fruitful topic in liquid crystal researches since ferro-, anti-ferroelectricity and chrality were found in such achiral moleculear systems. A number of banana-shaped liquid crystalline molecules have been synthesized and studied by particularly modifying of the well-known banana-shaped molecule 1,4-phenylene [4-(4-n-alkoxypheny liminomethyl)benzoates, P-n-O-PIMB, subsequently, a variety of liquid crystalline phases and interesting properties have been revealed. In this study, we prepare a new homologous series of banana-shaped molecule containing oxadiazole core,2,5-bis(4'-n-alkylcarboxy biphenyl-4-yl)-[1,3,4]-oxadiazole (ODBBP-n) to extend the study on the polymeric banana molecules. To our knowledge, this is the first example of five-membered heterocyclic liquid crystalline molecule that exhibits banana class mesophase. In addition, the relationship between the bending geometry and mesomorphic behavior of ODBBP-n is also demonstrated by comparing with thiaziazole core derivatives. The results obtained simply described below.1)From the analysis of chiral memory between B2 and B4 phases, it was concluded that the spontaneously arising chirality is due to the chiral conformation characteristic of the banana shape.2)In ferroelectric B2 phase, the distinct layer undulation takes place as a result of the interplay between the spontaneous polarization and layer elasticity.3)In the banana molecules with the asymmetric alkyl tails, it was found that antiferroelectric phase is altered to the ferroelectric phase when two tail groups have the remarkable difference in their length.4)The extension of the study to the polymeric system failed because of the high temperature melting of polymer. Now, we try to synthesize the dimer and trimer of banana molecules.