4-Methylresorcinol based bent-core liquid crystals with azobenzene wings – a new class of compounds with dark conglomerate phases
作者:Mohamed Alaasar、Marko Prehm、Marcel Brautzsch、Carsten Tschierske
DOI:10.1039/c4tc00533c
日期:——
Stochastic achiral symmetry breaking in soft matter systems, leading to conglomerates of macroscopically chiral domains (so-called dark conglomerate = DC phases) is of contemporary interest from a fundamental scientific point of view as well as for numerous potential applications in chirality sensing and non-centrosymmetric materials. Herein we report the synthesis and investigation of first azobenzene containing bent-core mesogens derived from 4-methylresorcinol forming DC phases with a new structure, distinct from the known fluid sponge-like distorted smectic phases as well as from the helical nano-filament phases (HNF phases, B4 phases). The effects of chain length and other structural modifications on achiral symmetry breaking were investigated. Homologues with relatively short alkyl chains form achiral intercalated lamellar LC phases (B6 phases), but on increasing the chains, these are replaced by the chiral and optically isotropic DC phases. Compounds with the longest alkyl chains form low birefringent crystalline conglomerates which represent less distorted versions of the optically isotropic DC-phases. Introducing additional peripheral substituents at both outer rings removes the DC phases. The DC phases were also removed and replaced by modulated smectic phases if the azo groups were replaced by ester units, showing that azo groups favour DC phase formation with new nanostructures, distinct from the previously known types.
软物质体系中的随机非手性对称破缺会导致宏观手性域的集合体(即所谓的暗集合体 = DC 相),从基础科学的角度以及手性传感和非中心对称材料中的众多潜在应用来看,这种破缺具有时代意义。在此,我们报告了第一种由 4-甲基间苯二酚衍生的含弯核中间体偶氮苯的合成与研究,这些中间体形成了具有新结构的 DC 相,有别于已知的流体海绵状扭曲构造相以及螺旋状纳米纤维相(HNF 相,B4 相)。我们研究了链长和其他结构修饰对非手性对称性破坏的影响。烷基链相对较短的同系物形成了非手性夹层片状低浓相(B6 相),但随着烷基链的增加,这些同系物被手性和光学各向同性的 DC 相所取代。烷基链最长的化合物会形成低双折射结晶团块,代表光学各向同性 DC 相的较小变形版本。在两个外环上引入额外的外围取代基可以消除直流相。如果将偶氮基团替换为酯单元,则直流相也会消失,取而代之的是调制的平滑相,这表明偶氮基团有利于形成具有新纳米结构的直流相,不同于之前已知的类型。