Effect of lateral substitution of different polarity on the mesophase behaviour in pure and mixed states of 4-(4′-substituted phenylazo)-2-substituted phenyl-4″-alkoxy benzoates

Abstract

Two groups of 4-(4′-substituted phenylazo)-2-phenyl-4″-alkoxy benzoates were prepared and their mesophase formation and stability investigated. Each group (I n _a-e and II n _a-e) constituted five homologous series differing in their terminal substituent, CH₃O, CH₃, H, Cl or NO₂. Within each series the number of carbons in the terminal alkoxy chain was 8, 10, 12, 14 or 16. The two main groups of compounds (I and II) differed in the polarity of the lateral substitutent attached to the central benzene ring. Group I had a chlorine atom adjacent to the ester group, replaced in Group II by the weakly electron-donating methyl group. Binary phase diagrams were constructed in which the two components were terminally-substituted analogues from within each group. The study was designed to investigate the effect of a lateral chloro or methyl group on the mesomorphic properties of the resulting derivatives, in pure or mixed states. The mesophase behaviour of the compounds themselves and their binary mixtures was investigated by differential scanning calorimetry and polarised light microscopy. The nematic phase was exhibited in most of the compounds, including their binary mixtures.

Keywords:

• lateral substitution
• binary mixtures
• 4-(4′-substituted phenylazo)-2-substituted phenyl-4″-alkoxy benzoates