Alaasar Mohamed, Darweesh Ahmed F, Cai Xiaoqian, Liu Feng, Tschierske Carsten
Institute of Chemistry, Martin Luther University Halle-Wittenberg, Kurt Mothes Str. 2, 06120, Halle (Saale), Germany.
Department of Chemistry Faculty of Science, Cairo University, Giza, Egypt.
Chemistry. 2021 Oct 25;27(60):14921-14930. doi: 10.1002/chem.202102226. Epub 2021 Oct 7.
Mirror symmetry breaking in systems composed of achiral molecules is of importance for the design of functional materials for technological applications as well as for the understanding of the mechanisms of spontaneous emergence of chirality. Herein, we report the design and molecular self-assembly of two series of rod-like achiral polycatenar molecules derived from a π-conjugated 5,5'-diphenyl-2,2'-bithiophene core with a fork-like triple alkoxylated end and a variable single alkylthio chain at the other end. In both series of liquid crystalline materials, differing in the chain length at the trialkoxylated end, helical self-assembly of the π-conjugated rods in networks occurs, leading to wide temperature ranges (>200 K) of bicontinuous cubic network phases, in some cases being stable even around ambient temperatures. The achiral bicontinuous cubic Ia d phase (gyroid) is replaced upon alkylthio chain elongation by a spontaneous mirror symmetry broken bicontinuous cubic phase (I23) and a chiral isotropic liquid phase (Iso * ). Further chain elongation results in removing the I23 phase and the re-appearance of the Ia d phase with different pitch lengths. In the second series an additional tetragonal phase separates the two cubic phase types.
由非手性分子组成的体系中的镜像对称性破缺对于技术应用功能材料的设计以及对手性自发出现机制的理解都很重要。在此，我们报告了两类棒状非手性多链节分子的设计与分子自组装，它们源自具有叉状三烷氧基化末端和另一端可变单烷硫基链的π共轭5,5'-二苯基-2,2'-联噻吩核心。在这两类液晶材料中，三烷氧基化末端链长不同，π共轭棒在网络中发生螺旋自组装，导致形成宽温度范围（>200 K）的双连续立方网络相，在某些情况下甚至在环境温度附近也稳定。非手性双连续立方Ia d相（类金刚石相）在烷硫基链伸长时会被自发镜像对称性破缺的双连续立方相（I23）和手性各向同性液相（Iso *）取代。进一步的链伸长导致I23相消失，不同螺距长度的Ia d相重新出现。在第二类材料中，一个额外的四方相将两种立方相类型分隔开来。
