POLYAZOMETHINE–ZN(II) COMPLEXES WITH TUNABLE THERMAL, ELECTROCHEMICAL AND ANTIMICROBIAL PROPERTIES: SYNTHESIS, CHARACTERIZATION AND STRUCTURE–PROPERTY RELATIONSHIPS

Abstract

Polyazomethines are π-conjugated Schiff-base polymers whose azomethine nitrogen atoms provide coordination sites for metal ions and thereby offer a convenient route to multifunctional materials. In the present study, four aromatic polyazomethines were synthesized by condensation of p-phthalaldehyde with 4,4′-diaminodiphenyl ether (ODA), 4,4′-diaminodiphenylmethane (DDM), 4,4′-diaminodiphenyl sulfone (DDS), and p-phenylenediamine (PPD). Corresponding Zn(II)-containing polymeric complexes were prepared using ZnCl₂ under reflux conditions. The products were examined by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), cyclic voltammetry (CV), and antimicrobial screening. FTIR spectra confirmed formation of the azomethine backbone through characteristic C=N stretching bands and showed additional changes attributable to Zn–N/Zn–O coordination. XRD indicated predominantly amorphous or weakly semicrystalline structures, while Zn incorporation increased the degree of local structural ordering, most markedly for the DDS- and PPD-derived systems. TGA demonstrated a clear improvement in thermal resistance after Zn coordination; the PPD-derived complex showed the highest reported thermal stability, with T₀, T₁₀, T₅₀ and T_max values of 346, 429, 547 and 600 °C, respectively, together with an 18% char residue. Cyclic voltammetry revealed scan-rate- and potential-window-dependent redox responses and generally good electrochemical cycling stability within the investigated ranges. Antimicrobial screening against Staphylococcus aureus, Escherichia coli and Candida albicans showed that the Zn-containing materials generally produced larger inhibition zones than their corresponding parent polymers, although the activity remained below that of the reference antimicrobial agents used in the study. Overall, the results demonstrate that Zn coordination provides an effective structural modification strategy for simultaneously tuning the thermal, electrochemical and antimicrobial characteristics of polyazomethines.