Effect of replacing the terminal phenyl ring with 3-pyridyl and inversion of imine linkage on the mesophase behaviour of four-ring azo/ester/Schiff base compounds

Abstract

ABSTRACT In the present work two homologue series of four-ring azo/ester/imine compounds; namely, 4-(4′–alkoxy–phenylazo) phenyl–4′′–(benzylidene–amino) benzoate, I n, and 4–(4′–alkoxy–phenylazo) phenyl–4′′–[(pyridin-3–ylmethylene)–amino] benzoate, II n, were prepared and investigated for their mesophase behaviour. In these two types of homologue series, the length of the terminal alkoxy group (n) varies between 6 and 16 carbons. Compounds prepared in both series were structurally characterised via thermogravimetric and elemental analyses, FTIR, 1H-NMR, and mass spectroscopy. Their mesophase transition temperatures were determined by differential scanning calorimetry (DSC), whereas, the type of the mesophase was identified by polarised light microscopy (PLM). The molecular structure–property relationship was conducted aiming to investigate the effect of replacing the terminal phenyl group in I n with a pyridyl one in II n, in addition to the effect of variation of the alkoxy chain length. Aiming to investigate the effect of inversion of the methineazo group on the mesophase behaviour of the compounds, a comparison was made between the prepared series of compounds (I n) with previously prepared four rings 4-(4′-alkoxyphenylazo)–phenyl 4′′–phenyliminomethyl–benzoate phenyl-4ʹ-(4′′-alkoxyphenylazo) benzoate, III n. Finally, the mesophases of series II n were compared with their corresponding three-ring analogues, 4-(4′-alkoxy phenyl −4′′-[(pyridin-4-ylmethylene)–amino] benzoate analogues (IV n).