Synthesis and characterization of fluorescent polyphenols anchored Schiff bases via oxidative polycondensation

A series of polyimines, bearing phenolic groups were successfully synthesized in aqueous alkaline solution via chemical oxidative polycondensation. Polymeric Schiff bases were synthesized by condensation of 2,4-dihydroxybenzaldehyde and 3-hydroxy-4-metoxybenzaldehyde with 2-aminophenol and 3-aminophenol. The molecular structures of the synthesized Schiff bases and their corresponding polymers were studied by FT-IR, UV-Vis, ¹H-NMR and ¹³C-NMR spectroscopic methods. Thermal stability of the imine polymers was evidenced by their initial degradation temperatures found in the range of 170 °C to 271 °C without any sign of melting. The results of UV-Vis and cyclic voltammetry (CV) measurements were coherent with the optical E_g and the electrochemical E′_g band gaps of the polyimines which were lower than those of their corresponding Schiff bases. Fluorescence spectral analysis of P4 (Schiff base polymer P4 derived from 3-aminophenol and 3-hydroxy-4-methoxybenzaldehyde) revealed a bicolor emission with blue and green light. Electrical conductivity of the synthesized imine polymers was measured by four-point probe technique. P4 showed the highest electrical conductivity as a result of iodine vapor contact time. Morphology characterization of the synthesized polyimines was carried out using a scanning electron microscope SEM at different magnifications. The study revealed that P4 is a promising candidate for both blue and green light emitters which could be used in the production of photovoltaic materials and solar cells.