Ten isomeric five-ring bent-core mesogens: The influence of the direction of the carboxyl connecting groups on the mesophase behaviour
作者:Wolfgang Weissflog、Gisela Naumann、Bedrich Kosata、Martin W. Schröder、Alexey Eremin、Siegmar Diele、Zinaida Vakhovskaya、Horst Kresse、Rudolf Friedemann、S. Ananda Rama Krishnan、Gerhard Pelzl
DOI:10.1039/b508488a
日期:——
In order to study the role of the direction of the connecting groups in bent-core mesogens we synthesized two series of ten possible achiral isomeric five-ring bent-core compounds in which all aromatic rings are connected by ester groups and each of which possesses the same length of the terminal chains (octyloxy or dodecyloxy, respectively). The structure of the isomers is distinguished by the direction of at least one ester group, only. The mesophase behaviour of the compounds has been studied by polarizing microscopy, differential scanning calorimetry, X-ray experiments and electro-optical measurements. We have found that in spite of the minor structural differences a variety of mesophases occur (SmCPA, Colrec, Colob) whereby the clearing temperatures vary from 121 to 193 °C (octyloxy isomers) and 112 to 189 °C (dodecyloxy isomers). Depending on the direction of the ester groups some of these isomers show interesting properties, such as field-induced inversion of chirality in SmCPA and columnar phases, the field-induced enhancement of the clearing temperature, a second-order phase transition Colob
→ SmCPA or the reversible field-induced phase transition Colob
→ SmCPF. The unexpectedly strong influence of the direction of the connecting groups is discussed on the base of theoretical calculations and molecular dynamics simulation on isolated molecules.
为了研究连接基团方向在弯核介素中的作用,我们合成了两个系列的十种可能的非手性异构五环弯核化合物,其中所有的芳香环都由酯基连接,每种化合物都具有相同长度的末端链(分别为辛氧基或十二氧基)。异构体的结构仅以至少一个酯基的方向来区分。我们通过偏光显微镜、差示扫描量热法、X 射线实验和电光测量等方法对这些化合物的介相行为进行了研究。我们发现,尽管结构上存在细微差别,但还是出现了多种介相(SmCPA、Colrec、Colob),其清除温度在 121 至 193 ℃(辛氧基异构体)和 112 至 189 ℃(十二烷氧基异构体)之间变化。根据酯基方向的不同,其中一些异构体显示出有趣的特性,如在 SmCPA 和柱状相中由场诱导的手性反转、由场诱导的清除温度升高、二阶相变 Colob → SmCPA 或可逆的场诱导相变 Colob → SmCPF。在对孤立分子进行理论计算和分子动力学模拟的基础上,讨论了连接基团方向意想不到的强烈影响。