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

研究了两个具有C3对称性和pi共轭取代基的[1，3，4]三氮杂并[1，3，5]三氮杂异构体的切向排列和径向排列。“切向”异构体在高温下的热处理会导致杂环体系的逐步重排。三氮唑的环化发生变化，取代基从原来的“切向”向“径向”方向移动。由此形成的“径向”-三氮杂三氮杂环是一种新型的盘状液晶杂环核心。合成这两种异构体的独立途径包括三嗪基酰胺和-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。为此目的，将制备第一个具有非对称核的三氮杂三嗪。结合给体和受体取代将区分三氮唑-三氮唑键，并揭示异构化步骤的选择性和顺序。将制备具有非对称外围的C3对称核心。采用混合烷基链长和混合取代方式对其热性能进行了研究。将制备史无前例的以苯乙烯基和二芳基-1，3，4-恶二唑为pi链段的三氮杂三氮类化合物：二芳基-1，3，4-恶二唑将导致严重缺乏电子的盘片，可用作n型半导体。苯乙酰取代打开了光化学的大门：[2 2]-溶液中的环加成反应可以生成环芳烃，在LC相中，光化学交联可以稳定色谱柱。三氮杂三氮类化合物是一类强发光的荧光团，能够形成宽广的热致性中间相。三氮杂三嗪的合成和重排伴随着对这些材料的光学、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.