Heptasubstituted triphenylene 2,3-dicarboxylic esters discotic liquid crystals with three different types of peripheral substitution |
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Authors: | Cheng-Yan Gan Jing Zhou Wen-Hao Yu Shi-Kai Xiang Lai-Cai Li Bi-Qin Wang |
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Institution: | College of Chemistry and Materials Science, Sichuan Normal University, Chengdu, Sichuan Province, P. R. China |
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Abstract: | Hexasubstituted triphenylene (1a) containing four alkoxy and two adjacent methoxycarbonyl tails can be smoothly brominated or nitrated at its α-position(s) of two electron-rich rings to give a series of bromides and nitro compounds through electrophilic aromatic substitutions. Positions of bromo or nitro groups in target compounds were unambiguously established by combined analysis of 2D nuclear magnetic resonance experiments including nuclear Overhauser effect and heteronuclear multiple-bond correlation which indicated that monobromination or mononitration occurred preferentially at position 8 or 5 of 1a, respectively. Calculations of molecular geometry on 2a–e reveal that the α-Br or α-NO2 group(s) would induce different degrees of helical deformation in the triphenylene core and the degree of non-planarity decrease in the following order: 2c > 2b > 2e > 2a > 2d. In contrast to highly twisted 2b–c and 2e, which did not form a mesophase, the formation of a hexagonal columnar phase at room temperature even down to ?50°C was observed and confirmed by polarising optical microscopy and X-ray diffraction for sterically less hindered, monosubstituted 2a and 2d. |
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Keywords: | Heptasubstituted triphenylene discotic liquid crystal helical deformation triphenylene 2 3-dicarboxylic ester |
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