Discotic Liquid Crystals based on Tristriazolotriazines: Synthesis, Properties and the tangential-radial Isomerization

研究了两种具有C3对称的[1,3,4]三氮唑[1,3,5]三嗪异构体，它们具有切向或径向排列的偶共轭取代基。切向异构体在高温下的热处理导致杂环体系的逐步重排。三唑的环向改变，取代基从原来的“切向”取向转变为“径向”取向。由此形成的“径向”-三三氮唑三嗪是一种新的盘状液晶杂环核。合成这两种异构体的独立途径包括三嗪酰胺和-肼的环缩合和氧化。异构化过程的优化与动力学和机理研究相结合。为此，将制备具有非对称核的第一种三氮唑三嗪类化合物。结合供体和受体取代将区分三唑-三唑键，并阐明异构化步骤的选择性和顺序。将制备具有非对称外围的c3对称芯。Míxed烷基链的长度和混合取代模式用于调整热性能。将制备前所未有的以苯乙烯-和二芳基-1,3,4-恶二唑为pi-节段的三三唑三嗪类化合物：二芳基-1,3,4-恶二唑将产生强电子亏缺盘，可用作n型半导体。苯乙烯取代打开了光化学的大门：[2+2]-环在溶液中的添加可以导致环烷，在lc相中，光化学交联可以稳定柱。三氮唑三嗪是强发射荧光团，具有形成广泛的热致中间相的能力。三三氮唑三嗪的合成和重排伴随着这些材料的光学、电学和热学性质的广泛表征，包括在中间相诱导螺旋手性的实验。

Two isomeric [1,3,4]tristriazolo[1,3,5]triazines with C3 symmetry and pi-conjugated substituents, either in a tangential or in a radial arrangement, are investigated. Thermal treatment of the `tangential`-isomer at elevated temperatures results in a stepwise rearrangement of the heterocyclic system. The annulation of the triazoles changes and the substituents are shifted from the original `tangential`- to a ´radial`-orientation. The thus formed ´radial`-tristriazolotriazine is a new heterocyclic core for discotic liquid crystals. Independent pathways for the synthesis of both isomers include cyclocondensation and oxidation of triazinylamides and -hydrazides.Optimisation of the isomerisation procedure is combined with kinetic and mechanistic studies. For this purpose, the first tristriazolotriazines with a non-symmetric core will be prepared. Combining donor- and acceptor substitution will discriminate the triazole-triazole bonds and shed light on the selectivity and sequence of the isomerisation steps. C3-symmetric cores with an asymmetric peripherie will be prepared. míxed lengths of the alkyl chains and mixed substitution pattern are used for a tuning of the thermal properties. Unprecedented tristriazolotriazines with styryl- and diaryl-1,3,4-oxadiazole as pi-segmente will be prepared: the diaryl-1,3,4-oxadiazole will result in strongly elektron deficient discs, usefuls as n-type semiconductors. Styryl-substitution opens the door to photochemistry: [2+2]-cycloadditions in solution can lead to cyclophanes, in the LC-Phase, photochemical cross-linking can stabilise the columns. Tristriazolotriazines are strongly emissive fluorophores with the ability to form broad thermotropic mesophases. The synthesis and rearrangement of tristriazolotriazines is acompanied by extensive characterisation of the optical, electrical and thermal properties of these materials, including experiments for the induction of helical chirality in the mesophase.