Functional star-shaped tris(triazolyl)triazines: columnar liquid crystal, fluorescent, solvatofluorochromic and electrochemical properties
作者:Eduardo Beltrán、José Luis Serrano、Teresa Sierra、Raquel Giménez
DOI:10.1039/c2jm15648b
日期:——
Columnar liquid crystals with a C3 star-shaped heteroaromatic nitrogen-rich core, i.e. 2,4,6-tris(1′,2′,3′-triazol-4′-yl)-1,3,5-triazine (TTT), that show luminescence and solvatofluorochromism, and are also electron-acceptors are described. The core has been extended with polyalkoxybenzoyloxyphenyl groups situated at the 1 position of the 1,2,3-triazole rings to obtain molecules with three, six or nine n-decyloxy chains (series TB) or three, six or nine (S)-3,7-dimethyloctyloxy chains (series TB*). The preparation of the target compounds involved a copper-catalysed alkyne–azide cycloaddition (CuAAC) “click chemistry” procedure with a 1,3,5-triazine precursor and aromatic azides and this proved to be a versatile way to functionalise the periphery of the heteroaromatic core. Comparison of these compounds and those bearing polyalkoxyphenyl substituents (series T) has led to a deeper understanding of the self-assembly of the compounds with the TTT core. It was found that they self-organise into columnar mesophases, in which two molecules with a low-symmetry conformation occupy on average a columnar stratum. These molecules tend to adopt a polar conformation instead of the apolar C3 conformation and arrange in an antiparallel assembly. For some compounds the molecules in this arrangement have enough flexibility to tilt upon lowering temperature or by applying an electric field. Interestingly, the hexagonal columnar arrangement is preserved in a glassy state at room temperature. Furthermore, the mesophases show luminescence in the blue region of the visible spectrum depending on the peripheral substitution and molecular structure. We also report a novel property of TTT compounds (series T, TB and TB*) as they are able to act as solvatofluorochromic probes, a property that allowed us to estimate the overall polarity of the liquid crystalline medium. An aromatic azide precursor was also found to be mesomorphic and exhibited a monolayer SmA mesophase.
本文描述了具有 C3 星形杂芳香族富氮核心(即 2,4,6-三(1′,2′,3′-三唑-4′-基)-1,3,5-三嗪 (TTT))的柱状液晶,这种液晶具有发光和溶解氟变色功能,同时也是电子受体。通过在 1,2,3-三唑环的 1 位上添加多烷氧基苯甲酰氧基苯基基团,扩展了该核心,从而获得了具有 3、6 或 9 个正癸氧基链(系列 TB)或 3、6 或 9 个(S)-3,7-二甲基辛氧基链(系列 TB*)的分子。目标化合物的制备涉及铜催化的炔吖啶环加成(CuAAC)"点击化学 "过程,使用 1,3,5-三嗪前体和芳香族叠氮化物。通过比较这些化合物和带有多烷氧基苯基取代基(T 系列)的化合物,我们对带有 TTT 核心的化合物的自组装有了更深入的了解。研究发现,这些化合物自组织成柱状介相,其中具有低对称性构象的两个分子平均占据一个柱状层。这些分子倾向于采用极性构象,而不是无极性的 C3 构象,并以反平行排列。对于某些化合物来说,这种排列方式的分子具有足够的灵活性,在温度降低或施加电场时会发生倾斜。有趣的是,六角柱状排列在室温下的玻璃态中得以保留。此外,根据外围取代和分子结构的不同,介相还会在可见光谱的蓝色区域发光。我们还报告了 TTT 化合物(系列 T、TB 和 TB*)的一个新特性,即它们能够作为溶解氟变色探针,这一特性使我们能够估计液晶介质的整体极性。我们还发现一种芳香叠氮前体具有介形性,并表现出单层 SmA 介相。