Dressel Christian, Liu Feng, Prehm Marko, Zeng Xiangbing, Ungar Goran, Tschierske Carsten
Institute of Chemistry, Organic Chemistry, Martin-Luther-University Halle-Wittenberg, Kurt-Mothes-Str. 2, 06120 Halle (Germany).
Angew Chem Int Ed Engl. 2014 Nov 24;53(48):13115-20. doi: 10.1002/anie.201406907. Epub 2014 Sep 26.
Chiral segregation of enantiomers or chiral conformers of achiral molecules during self-assembly in well-ordered crystalline superstructures has fascinated chemists since Pasteur. Here we report spontaneous mirror-symmetry breaking in cubic phases formed by achiral multichain-terminated diphenyl-2,2'-bithiophenes. It was found that stochastic symmetry breaking is a general phenomenon observed in bicontinuous cubic liquid crystal phases of achiral rod-like compounds. In all compounds studied the Im3̄m cubic phase is always chiral, while the Ia3̄d phase is achiral. These intriguing observations are explained by propagation of homochiral helical twist across the entire networks through helix matching at network junctions. In the Ia3̄d phase the opposing chiralities of the two networks cancel, but not so in the three-networks Im3̄m phase. The high twist in the Im3̄m phase explains its previously unrecognized chirality, as well as the origin of this complex structure and the transitions between the different cubic phases.
自巴斯德时代以来，非手性分子的对映体或手性构象在有序晶体超结构自组装过程中的手性分离就一直吸引着化学家。在此，我们报道了由非手性多链端基二苯基-2,2'-联噻吩形成的立方相中的自发镜像对称破缺。研究发现，随机对称破缺是在非手性棒状化合物的双连续立方液晶相中观察到的普遍现象。在所研究的所有化合物中，Im3̄m立方相总是手性的，而Ia3̄d相是非手性的。这些有趣的观察结果可以通过在网络节点处通过螺旋匹配使同手性螺旋扭曲在整个网络中传播来解释。在Ia3̄d相中，两个网络相反的手性相互抵消，但在三网络Im3̄m相中并非如此。Im3̄m相中的高扭曲解释了其先前未被认识到的手性，以及这种复杂结构的起源和不同立方相之间的转变。
