Dithiophene based X-shaped bolaamphiphiles: liquid crystals with single wall honeycombs and geometric frustration
作者:Hongfei Gao、Yafei Ye、Leiyang Kong、Xiaohong Cheng、Marko Prehm、Helgard Ebert、Carsten Tschierske
DOI:10.1039/c2sm26575c
日期:——
A series of 5,5′-diphenyl-2,2′-dithiophene based X-shaped polyphiles with two long lateral alkyl chains and terminal glycerol groups was synthesized and the liquid crystalline phases formed by these compounds were investigated by polarizing microscopy, DSC and XRD. These compounds form square (p4mm and p4gm) and hexagonal (p6mm) columnar LC phases. In these mesophases the molecules organize into polygonal honeycombs where the π-conjugated cores form the walls, fused at the edges by the hydrogen bonding networks between the glycerol units and filled by the lateral alkyl chains. By elongation of these chains, a series of polygonal honeycomb phases with a “single wall” structure, ranging from triangular via square and pentagonal to hexagonal was observed. Most triangular honeycombs appear to be defective and can be considered as mixtures of triangular cylinders with orientationally randomized rhombic cylinders. The transition from this improper triangular honeycomb to the square honeycomb takes place via a disordered isotropic phase. Addition of water to this isotropic phase gives rise to a true triangular honeycomb LC phase. Replacing one of the long lateral chains by a small methyl group leads to honeycombs formed by double walls instead of single walls. UV investigations indicate π-stacking of the aromatic cores organized in the honeycomb walls, which is of interest for the potential application of these materials in self assembled arrays of organic electronic material.
合成了一系列基于5,5′-二苯基-2,2′-二硫代苯的X形聚合物,这些聚合物具有两个长侧链和端部甘油基团,并对这些化合物形成的液晶相进行了偏光显微镜、差示扫描量热法(DSC)和X射线衍射(XRD)研究。这些化合物形成了方形(p4mm和p4gm)和六角形(p6mm)柱状液晶相。在这些中间相中,分子组织成多边形蜂窝结构,π共轭核心形成墙壁,通过甘油单元之间的氢键网络在边缘连接,侧链则填充其中。通过延长这些链,观察到一系列具有“单墙”结构的多边形蜂窝相,形状从三角形到方形、五边形再到六角形。大多数三角形蜂窝似乎是缺陷结构,可以视为带有方向随机的菱形柱体的三角形柱体的混合体。这个不规则的三角形蜂窝到方形蜂窝的转变是通过一个无序的各向同性相进行的。向该各向同性相中添加水会产生一个真正的三角形蜂窝液晶相。用小的甲基取代其中一个长侧链会导致蜂窝形成双墙而不是单墙。紫外线研究表明,芳香核心在蜂窝墙中的堆叠现象,这对这些材料在自组装有机电子材料阵列中的潜在应用具有重要意义。