Investigation of the effect of bulky lateral substituents on the discotic mesophase behaviour of triphenylene benzoates

Abstract

Lateral substitution in the peripheral phenyl groups of the triphenylen-2,3,6,7,10,11-hexayl hexakis(4-alkoxybenzoate)s was investigated via substitution of methyl, ethyl, isopropyl and tert-butyl groups ortho to either the peripheral alkoxy chain or the internal ester linking group. The discotic mesogenic compounds were prepared by the esterification of 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) with the respective 3-alkyl- or 2-alkyl-4-decyloxybenzoyl chlorides (alkyl = methyl, ethyl, isopropyl or tert-butyl) in the presence of pyridine. Thermal polarized light microscopy and differential scanning calorimetry were used to investigate the liquid-crystalline behaviour of the materials prepared. Suppression of columnar mesophases was observed for both series. A general increase in the clearing temperatures was observed for the outer-substituted series when the size of the lateral substituent was increased, but a depression of the clearing points was found for the inner-substituted series. These observations were investigated through molecular modelling.