Synthesis and mesophase behaviour of Schiff base/ester 4-(arylideneamino)phenyl-4″-alkoxy benzoates and their binary mixtures

Abstract

Four new groups of Schiff base ester liquid crystal compounds, 4-(arylideneamino)phenyl-4″-alkoxy benzoates, Ina–d, were prepared and investigated for their mesophase formation and stability. An alkoxy group of variable chain length (n = 6, and 16 carbons) is attached to the terminal phenylazo benzoate moiety. Each group constitutes two homologous series that differ from each other by the polar substituent X (CH3O, H, NO2, and F). The molecular structure of the prepared compounds was confirmed via FT-IR, 1H NMR, mass spectroscopy and elemental analysis. The mesomorphic properties were investigated by differential scanning calorimetry (DSC) and polarized light microscopy (PLM). For n = 6, all compounds exhibit nematic phase. Amongst them methoxy and nitro derivatives have widest mesophase range. For n = 16, nitro and flouro derivatives exhibit SmA phase, while methoxy and unsubstituted derivative are nematogenic. The change of the mesophase stability is well correlated with van der Waals volume and polarizability of the substituent X and not satisfactory with the dipole moment of the whole molecule. The mesophase behavior of binary mixtures made from each individual derivatives bearing the same substituent X but varies with alkoxy chains length is presented. Results provide insights into the role of substituent X and alkoxy chain length on the mesophase behavior within the whole composition range of the mixtures.