Lateral substitution in the peripheral moieties of triphenylen-2,3,6,7,10,11-hexayl hexakis(4-alkoxybenzoate)s: dimethyl-substituted systems

Abstract

Lateral substitution in the peripheral phenyl groups of the triphenylen-2,3,6,7,10,11-hexayl hexakis(4-alkoxybenzoate)s has been investigated via dimethyl substitution ortho to the terminal alkoxy chain or the ester linking group. Similarly, lateral methyl substitution in the terminal alkoxy chain was also investigated. The discotic mesogenic compounds were prepared by the esterification of 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) with the respective 4-alkoxy-3,5- or 4-alkoxy-2,6-dimethylbenzoyl chlorides 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. The compounds with dimethyl substitution in the 3 and 5 positions in the peripheral phenyl rings were found to exhibit the hexagonal disordered (D_hd) columnar mesophase and the discotic nematic mesophase (N_D), whereas the analogous compounds with substitution at the 2 and 6 positions only exhibited discotic nematic (N_D) mesophases. Thus, methyl substitution was found to suppress totally columnar phase formation in the second series of compounds, where the methyl groups were positioned pointing in towards the triphenylene core.