The influence of heteroatoms and branchings on the liquid-crystalline properties of cyclotriveratrylene derivatives

The synthesis and properties of novel pyramidic liquid crystals are reported. 2,3,7,8,12,13-Hexaacyloxy-10, 15-dihydro-5H-tribenzo [a,d,g]cyclononenes incorporate heteroatoms (O or S) in different positions in the lateral chains. The mesomorphic properties of these compounds were investigated by polarizing light microscopy, calorimetry and X-ray scattering. Most of the compounds display broad ranges of different columnar mesophases (D-hd, D-rd, D-ob). It was found that the mesophase stability of the 3-oxaalkanoates is increased in comparison to the analogous alkanoates. However, the shift of the oxygen atoms into the 4 positions leads to a destabilization of the mesophases. The 3-thiaalkanoate displays approximately the same clearing temperature as the corresponding carbon analogue. Branching of the lateral chains gives rise to discotic liquid crystals with broad mesomorphic ranges and increased clearing temperatures, compared to the corresponding non-branched derivatives.