Synthesis and characterization of new thermally stable, antimicrobial and red-light-emitting poly(azomethine-ester)s

Abstract

Two new diphenol Schiff base monomers were prepared through condensation reaction between 4-hydroxybenzaldehyde and 4,4′-diaminodiphenyl sulfone (dapsone) or 1,2-cyclohexanediamine. The resulting Schiff bases were reacted with terephthaloyl dichloride through polycondensation and formed two novel poly(azomethine-ester)s. The molecular masses of diphenol Schiff bases were determined through E.I mass spectroscopy. The elemental composition of poly(azomethine-ester)s was evaluated through CHN analysis. The structures of diphenol Schiff bases and poly(azomethine-ester)s were confirmed though FT-IR, 1HNMR, UV–Vis spectroscopy, fluorescence, SEM and thermal analysis (TG/DTA). All the synthesized compounds were fluorescent and indicated 2–4 emission bands with maximum emission intensities within 342–682 nm at different excitation wavelengths. The diphenol Schiff bases showed violet-light emission, while their derived polyesters showed red-light emission. The poly(azomethine-ester)s indicated good thermal stability (347 °C and 561 °C) which was estimated through $$T_{ \hbox{max} }$$ (temperature at which rate of weight loss is maximum) value obtained from DTG (derivative thermogravimetry) graph. The synthesized compounds were also tested for their antimicrobial activities against different species of bacteria and fungi. The Schiff base having dapsone moiety showed 55% inhibition, while its derived poly(azomethine-ester) showed 40% inhibition against bacterial species Shigella flexneri.