The dramatic influence of the location of bend and of lateral fluoro substitution on the mesomorphic properties of angular chiral esters based on a 1,3-disubstituted benzene ring
作者:Kenneth M. Fergusson、Michael Hird
DOI:10.1039/b923267b
日期:——
The synthesis and mesomorphic properties of a range of 3-ring and 4-ring chiral esters based on a 1,3-disubstituted benzene unit are detailed. These materials all deviate from the usual linear molecular architecture of liquid crystals, and hence are all angular in nature. Some of these materials have the bend right at the end of the molecule where the chain deviates from the normal linear arrangement, and hence a ‘hockey stick’ molecular architecture is perhaps an accurate description. Other materials have a genuine bent-core construction where the bend is towards the centre of the molecule, and hence are best termed as ‘boomerang’ shape. In all cases, interesting comparisons of mesophase morphology and transition temperatures were found, both between the various angular materials and with their linear analogues. In particular, the influence on transition temperatures of lateral fluoro substitution in the novel angular materials was found to be wholly different to that found in the known linear analogues. The work forms part of a larger on-going research programme to investigate the mesomorphic and chirality-dependent properties of angular liquid crystals. The research revealed that no mesomorphism in parent compounds is possible when the bend is close to the centre of the molecule, however, lateral fluoro substitution of such compounds facilitates the generation of liquid crystal phases. Where the molecular bend is as a consequence of the terminal unit at the end of the core, then surprisingly high clearing points resulted, and such materials were found to show the potential for a high tilt angle, and a strong tendency towards helical mesophases. Lateral fluoro substitution of these latter examples resulted consistently in significantly higher clearing points, which is in marked contrast to the behaviour reported previously in known liquid crystals of linear molecular architectures.
本文详细描述了一系列基于1,3-二取代苯单元的3环和4环手性酯的合成及其介态特性。这些材料都偏离了液晶的常规线性分子结构,因此具有角度特性。其中一些材料的弯曲位于分子末端,链条偏离正常线性排列,因此可以准确描述为“曲棍球棒”分子结构。其他材料则具有真正的弯曲核结构,弯曲指向分子的中心,因此最好称为“回旋镖”形状。在所有情况下,各种角度材料之间以及与其线性类似物之间的介相形态和转变温度进行了有趣的比较。特别是,在新型角态材料中,侧向氟 substituion 对转变温度的影响与已知线性类似物中的结果有显著不同。该研究工作是一个更大正在进行的研究项目的一部分,旨在探讨角液晶的介态和手性依赖特性。研究表明,当弯曲靠近分子的中心时,母体化合物中不可能出现介态。然而,这类化合物的侧向氟替代促进了液晶相的生成。当分子的弯曲是由于核心末端的末端单元引起时,则意外地得到了高清晰度点,同时这种材料显示出高倾斜角的潜力,以及强烈的螺旋介相倾向。对这些后者例子的侧向氟替代一致性地导致了明显更高的清晰度点,这与已知线性分子结构液晶中报告的行为形成了鲜明对比。