Cao Yu, Zhao Yangyang, Tan Tianyi, Liu Feng, Alaasar Mohamed
Shaanxi International Research Center for Soft Matter, State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, 710049, P. R. China.
Guangdong Provincial Key Laboratory of Functional and Intelligent Hybrid Materials and Devices, Guangzhou, 510641, China.
Chemistry. 2025 Jan 2;31(1):e202403586. doi: 10.1002/chem.202403586. Epub 2024 Nov 13.
Bicontinuous cubic liquid crystalline (LC) phases are of particular interest due their possible applications in electronic devices and special supramolecular chirality. Herein, we report the design and synthesis of first examples of achiral bent-shaped polycatenar dimers, capable of displaying mirror symmetry breaking in their cubic and isotropic liquid phases. The molecules have a taper-shaped 3,4,5-trialkoxybenzoate segment connected to rod-like building unit terminated with one terminal flexible chain. The two segments were connected using an aliphatic spacer with seven methylene units to induce bending of the whole structure. Investigated by the small-angle X-ray scattering (SAXS), a double network achiral cubic phase Cub/Ia d, which is a meso-structure, and a chiral triple network cubic phase Cub/I23* are formed. The molecules self-assemble into molecular helices and progress along the networks. Interestingly, different linking groups such as ester or azo linkages and core fluorination lead to distinct local helicity, resulting in an alkyl chain volume dependent phase transition sequence Ia d(L) - I23* - Ia d(S). The re-entry of Ia d phase and loss of supramolecular chirality is attributed to the delicate influence of steric effect at the mono-substitute end and interhelix interaction. Besides, aromatic core fluorination was proved to be a successful tool stabilizing the cubic phases in these dimers.
双连续立方液晶（LC）相因其在电子器件和特殊超分子手性方面的潜在应用而备受关注。在此，我们报道了首例非手性弯曲型多链节二聚体的设计与合成，该二聚体在立方相和各向同性液相中能够表现出镜像对称性破缺。这些分子具有一个锥形的3,4,5 - 三烷氧基苯甲酸酯片段，连接到一个末端带有一条柔性链的棒状结构单元上。这两个片段通过一个含有七个亚甲基单元的脂肪族间隔基相连，以诱导整个结构发生弯曲。通过小角X射线散射（SAXS）研究发现，形成了一种双网络非手性立方相Cub/Ia d，它是一种介观结构，以及一种手性三网络立方相Cub/I23*。分子自组装成分子螺旋并沿着网络排列。有趣的是，不同的连接基团如酯键或偶氮键以及核心氟化作用会导致不同的局部螺旋度，从而产生一种依赖于烷基链体积的相变序列Ia d(L) - I23* - Ia d(S)。Ia d相的再次出现和超分子手性的丧失归因于单取代端的空间效应和螺旋间相互作用的微妙影响。此外，芳香核氟化被证明是稳定这些二聚体中立方相的一种成功方法。
