Kang Sungmin, Saito Yuki, Watanabe Nobuhiro, Tokita Masatoshi, Takanishi Yoichi, Takezoe Hideo, Watanabe Junji
Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152, Japan.
J Phys Chem B. 2006 Mar 23;110(11):5205-14. doi: 10.1021/jp057307a.
Bent-shaped molecules based on the oxadiazole central core with various side wings and terminal chain groups have been synthesized, and their liquid-crystalline behavior was investigated by optical microscopic, X-ray, and electrooptic measurements. These molecules exhibit liquid-crystal polymorphism including both the calamitic and banana phases. Such a characteristic polymorphism is attributable to the larger bend angle of the oxadiazole core compared to that of the resorcinol core used in conventional banana molecules. Only one type of banana phase, designated as the Bx phase, is formed. It appears upon cooling from the nematic and smectic liquid crystals and exhibits chiral domains with a very weak birefringence (apparently optically isotropic). By applying an electric field, the Bx phase is altered to a high-birefringence B2 phase with a homochiral SmC(A)P(A) structure that exhibits an antiferroelectric response. From detailed analyses of the optical texture and X-ray patterns through the transformation from well-oriented calamitic phases, the Bx phase was found to exhibit a helical structure, which arises as a frustration from the ground-state B2 phase in such a manner that the blocks of B2 layers are twisted with respect to each other in a direction parallel to the layer plane similarly to the twisted grain boundary (TGB) phase.
基于恶二唑中心核以及各种侧翼和末端链基团合成了弯曲形分子，并通过光学显微镜、X射线和电光测量研究了它们的液晶行为。这些分子呈现出包括向列相和香蕉相的液晶多态性。这种特征性的多态性归因于恶二唑核的弯曲角比传统香蕉分子中使用的间苯二酚核的弯曲角更大。仅形成一种类型的香蕉相，称为Bx相。它在从向列相和近晶相液晶冷却时出现，并表现出具有非常弱双折射的手性畴（显然光学各向同性）。通过施加电场，Bx相转变为具有同手性SmC(A)P(A)结构且表现出反铁电响应的高双折射B2相。通过对通过从取向良好的向列相转变得到的光学织构和X射线图案的详细分析，发现Bx相呈现螺旋结构，这种结构是由于基态B2相的受挫而产生的，其方式是B2层的块在平行于层平面的方向上相对于彼此扭曲，类似于扭曲晶界（TGB）相。
