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

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.