Effect of lateral bromo substituent on the phase behavior of four-ring azo/ester/azo liquid crystalline materials

Abstract

ABSTRACTIn order to study the influence of lateral Br substitution on mesophase behaviour, five homologous series of 4-substituted phenylazo phenyl 4ʹ-(3ʺ-bromo-4ʺ-alkoxyphenylazo) benzoates (Ina–e) have been synthesised. Within each homologous series, the alkoxy group varies from 6 to 16 carbons, while other terminal group substituents, X, are CH3O, CH3, H, Br and NO2 groups; the mesophase behaviour of these series is compared with previously prepared laterally neat analogues, 4-substituted phenylazo phenyl 4ʹ-(4ʺ-alkoxyphenylazo) benzoates (IIna–e) and laterally methyl analogues, 4-substituted phenylazo phenyl 4ʹ-(3ʺ-methyl-4ʺ-alkoxyphenylazo) benzoates (IIIna–e). Similar to lateral methyl analogues, the present series, lateral Br substitution showed that, independent of the polarity of the substituent X or the alkoxy-chain length, the nematic phase is predominant with relatively high stability and broad temperature ranges. The mesophase stability varies between 204.0°C and 335.0°C for the nematic phase and 169.6°C and 281.0°C for the SmA phase. Their total mesophase temperature ranges vary between 87.2°C and 201.4°C. All compounds were found to be thermally stable within the mesophase temperature range, except the lower homologue of the nitro and Br substituted derivatives. The obtained results are discussed in terms of molecular polarisability.