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首页> 外文期刊>Chemistry: A European journal >Enantiotropic nematics from cross-like 1,2,4,5-tetrakis(4'-alkyl-4- ethynylbiphenyl)benzenes and their biaxiality studies
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Enantiotropic nematics from cross-like 1,2,4,5-tetrakis(4'-alkyl-4- ethynylbiphenyl)benzenes and their biaxiality studies

机译：十字形1,2,4,5-四（4'-烷基-4-乙炔基联苯）苯的对映向列型及其双轴性研究

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摘要

The theoretically predicted optimum length/breadth/width ratio for maximizing shape biaxiality was investigated experimentally by the facile and successful synthesis of cross-shaped compound 3, which showed enantiomeric nematic phase behavior. This cross-like core structure could alternatively be viewed as two fused V-shaped mesogens, which have recently immerged as a new direction in biaxial nematic research, at the bending tips that can act as a new structure for biaxial investigations. Whilst the thermal analysis data of compound 3 did not meet the expected theoretical values for biaxial nematics, surface-induced biaxiality was evidenced by optical studies. Cluster-size analysis within the nematic phase of compound 3 revealed the formation of meta-cybotactic nematics, which approached the cluster sizes of cybotactic nematics. The split small-angle 2D X-ray diffraction patterns of magnetic-field-aligned samples indicated that the nematic phase was composed of small smectic C-like clusters with the tilting of molecules within the clusters. The wide-temperature-range enantiomeric nematic phase of cross-like compound 3 enabled the molecular skeleton to serve as an alternative skeleton to bent-rod mesogens, which exhibited nematic phases with the potential competition of transitions to higher-order liquid-crystalline phases and crystallization, for future biaxial investigations. Take up your cross: An enantiotropic nematic phase with a wide temperature range has been achieved by using cross-like mesogens. Biaxiality investigations by using conoscopic and 2D XRD studies imply the formation of small smectic C-like meta-cybotactic clusters in the nematic arrangement.
机译：通过方便且成功地合成十字形化合物3来研究理论上预测的最大化形状双轴性的最佳长/宽/宽比，该化合物表现出对映异构向列相行为。这种十字形的核心结构也可以看作是两个融合的V形介晶，最近在双轴向列研究中浸入了一个新的方向，弯曲尖端可以作为双轴研究的新结构。尽管化合物3的热分析数据未达到双轴向列型的预期理论值，但光学研究证明了表面诱导的双轴性。化合物3向列相内的簇大小分析揭示了元-向列向列型的形成，其接近了向列向列型向列的簇大小。磁场对准样品的分裂小角度2D X射线衍射图表明，向列相由小的近晶C状簇组成，簇内分子倾斜。十字形化合物3的宽温度范围对映体向列相使分子骨架能够作为弯杆型液晶元的替代骨架，后者表现出向列相，并可能竞争向高阶液晶相的跃迁。结晶，以备将来进行双轴研究。拿起十字架：通过使用类似十字架的液晶元，可以实现宽温度范围的对映向列相。使用锥光镜和二维XRD研究进行的双轴性研究表明，向列排列中形成了小近晶状的C类超分子簇。

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