Department of Chemistry, Tamkang University, 251 Taipei, Taiwan.
Chemistry. 2012 Jul 27;18(31):9543-51. doi: 10.1002/chem.201103453. Epub 2012 Jun 28.
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.
通过简便且成功地合成具有手性向列相行为的十字形化合物 3，实验研究了最大化形状双轴性的理论预测的最佳长度/宽度比。这种十字形核心结构可以看作是两个融合的 V 形介晶，它们作为双轴向列研究的一个新方向，在弯曲尖端，可以作为双轴研究的新结构。虽然化合物 3 的热分析数据不符合双轴向列的预期理论值，但光学研究证明了表面诱导的双轴性。化合物 3 的向列相中的团簇尺寸分析表明形成了超团簇向列相，其接近超团簇向列相的团簇尺寸。磁场排列样品的分裂小角 2D X 射线衍射图案表明，向列相由小的类似 smectic C 的簇组成，分子在簇内倾斜。十字形化合物 3 的宽温度范围手性向列相使分子骨架能够作为弯曲棒状介晶的替代骨架，其向列相可能与向更高阶液晶相和结晶的转变竞争，用于未来的双轴研究。
