An Homologous Series of Disc-Like Mesogens with Nematic and Columnar Polymorphism

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Abstract
An homologous series of hexa alkoxybenzoates of triphenylene has been prepared with n = 4 to n = 12. Interphase transitions between solid, mesomorphic and isotropic phases were studied by hot stage microscopy and differential scanning calorimetry. Binary phase diagram studies, optical textures observations and X-ray measurements showed the existence of three different mesomorphic phases: a nematic disc-like phase N D, a tilted columnar phase D t and a rectangular disordered columnar phase D rd. Only two different phases were observed in each compound and the following mesophase sequences were found. This remarkable even-odd effect is discussed and is compared to that observed for classic liquid crystals. Several hexa alkybenzoates of triphenylene (n = C7 − C10) were also prepared and their mesomorphic properties studied. Only short range N D were observed.