At the Limits of Liquid Crystallinity: Stimuli Responsive 3D Columnar Liquid Crystals and Soft Crystals of Supramolecular Anthracene Mesogens
At the Limits of Liquid Crystallinity: Stimuli Responsive 3D Columnar Liquid Crystals and Soft Crystals of Supramolecular Anthracene Mesogens
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DOI：
10.1021/acs.chemmater.5b03382
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发表时间：
2015-12-22
影响因子：
8.6
通讯作者：
Roth, Sabine
中科院分区：
文献类型：
--
作者：
Lehmann, Matthias;Gloza, Steffi;Roth, Sabine
蒽在材料科学中被称为显示高荧光的发色团、1 液晶的刺激响应荧光、2− 4 可逆光化学、5 高载流子迁移率 6 并且它们是经过充分研究的有机凝胶剂。 7 大多数已知的蒽介晶在 9、10-2、4、8−10 上对称取代，很少在 2、6-位 3、11、12 上取代，并表现出向列或近晶介晶现象。当连接大的树枝状基团时，获得柱状和立方相。 2 对于这些材料，刺激响应发射特性最近被描述为与热或机械诱导的相变相关。 2− 4, 13, 14 我们在这里报告了第一个不对称的2, 6-取代蒽介晶1（图1），通过前所未有的横向氢键网络形成三维相关柱状液晶相。对化合物1的光物理性质的研究揭示了薄膜中的准分子发射，从高温下的青色变为室温下的绿色。与之前的报告相反，2−4 发射的变化与相变无关。由于温度升高或室温下紫外光照射时形成光产物而引起的紊乱会改变发射颜色。辐照还会导致 LC 相受到抑制；然而，1的LC自组装在黑暗退火后可以可逆地恢复。相比之下，对于化合物2来说，一个小的结构变化，羧基连接基被亚甲氧基连接基交换，导致环酸二聚体作为单独的结构单元，它们专门排列在柔软的condis晶体中，该晶体被定义为构象无序的结晶中间相。 15传统上，已知羧酸衍生物可形成环状二聚体。 16 一些带有柔性链的芳香酸是前介晶，它们需要分层排列在棒状二聚体超介晶中，以便随后组装在液晶结构中。 IR研究证实了氢键。 17−19 这种具有 5 至 6 个外围脂肪链的二聚体是 phasmidic 介晶，仅与形状各向异性结构单元中的约 5 个芳香族单元形成中间相。 20, 21 蒽的长度
Anthracenes are known in materials science as chromo-phores showing high fluorescence, 1 stimuli responsive fluorescence of liquid crystals, 2− 4 reversible photochemistry, 5 high charge carrier mobility 6 and they are well studied organo gelators. 7 Most of the known anthracene mesogens are symmetrically substituted in 9, 10-2, 4, 8− 10 and more rarely in 2, 6-position 3, 11, 12 and exhibit nematic or smectic mesomorphism. Columnar and cubic phases are obtained, when large dendritic groups are attached. 2 For these materials, stimuli responsive emission properties have been recently described to be related to thermal or mechanical induced phase transitions. 2− 4, 13, 14 We report here on the first unsymmetric 2, 6-substituted anthracene mesogen 1 (Chart 1) forming threedimensional correlated columnar liquid crystal phases by an unprecedented lateral hydrogen bonding network. The investigations of the photophysical properties of compound 1 reveal excimer emission in thin films, changing from cyan at high temperature to green at room temperature. In contrast to previous reports, 2− 4 the alteration in emission is not related to phase transitions. Disorder caused either by increasing the temperature or by the formation of photoproducts upon irradiation with UV light at room temperature switches the emission color. Irradiation leads also to the suppression of the LC phase; however, the LC self-assembly of 1 can be recovered reversibly after annealing in the dark. In contrast, for compound 2 a small structural change, the carboxy linker is exchanged by a methyleneoxy linker, leads to cyclic acid dimers as individual building blocks, which arrange exclusively in soft, condis crystals, which are defined as conformationally disordered crystalline mesophases. 15Conventionally, carboxylic acid derivatives are known to form cyclic dimers. 16 Some aromatic acids with attached flexible chains are promesogens, which need to arrange hierarchically in rod-shaped dimer supermesogens in order to assemble subsequently in liquid crystal structures. The hydrogen bonding was confirmed by IR studies. 17− 19 Such dimers with five to six peripheral aliphatic chains are phasmidic mesogens, which form mesophases only with about five aromatic units in the shapeanisotropic building block. 20, 21 The length of an anthracene