Apolar Bimesogens and the Incidence of the Twist-Bend Nematic Phase
Apolar Bimesogens and the Incidence of the Twist-Bend Nematic Phase
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DOI：
10.1002/chem.201500423
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发表时间：
2015-05-26
影响因子：
4.3
通讯作者：
Goodby, John W.
中科院分区：
文献类型：
--
作者：
Mandle, Richard J.;Davis, Edward J.;Goodby, John W.
直到最近，仅观察到极性介晶二聚体、三聚体或非极性核化合物的双扭-弯曲相（N-TB）。在这篇文章中，我们报告了一个全面的研究新型非极性材料，也表现出N-TB相。N-TB相被观察到的材料含有苯基，环己基或双环辛基环在其刚性核心单元。然而，对于具有长（>C7）末端链或包含三个环单元的介晶核单元的材料，未观察到N-TB相，相反，材料表现出近晶相。发现一种化合物表现出从N-TB相到背斜近晶C相的转变;这是这种多晶型的第一个例子。相对于中央核心单元的横向取代的并入导致转变温度的降低;然而，N-TB相仍然被发现发生。相反，利用支链端基使得材料非介晶。总的来说，似乎是总的分子拓扑结构驱动了N-TB相的发生，而不是简单的偶极考虑。此外，二聚体缺乏任何极性基团，这是准备测试这一假设，被发现是非介晶，表明在极性的极端，这些影响可以支配拓扑结构。
The nematic twist-bend phase (N-TB) was, until recently, only observed for polar mesogenic dimers, trimers or bent-core compounds. In this article, we report a comprehensive study on novel apolar materials that also exhibit N-TB phases. The N-TB phase was observed for materials containing phenyl, cyclohexyl or bicyclooctyl rings in their rigid-core units. However, for materials with long (>C7) terminal chains or mesogenic core units comprising three ring units, the N-TB phase was not observed and instead the materials exhibited smectic phases. One compound was found to exhibit a transition from the N-TB phase to an anticlinic smectic C phase; this is the first example of this polymorphism. Incorporation of lateral substitution with respect to the central core unit led to reductions in transition temperatures; however, the N-TB phase was still found to occur. Conversely, utilising branched terminal groups rendered the materials non-mesogenic. Overall, it appears that it is the gross molecular topology that drives the incidence of the N-TB phase rather than simple dipolar considerations. Furthermore, dimers lacking any polar groups, which were prepared to test this hypothesis, were found to be non mesogenic, indicating that at the extremes of polarity these effects can dominate over topology.