Comparative experimental and DFT study of the electrochemical oxidation of azo pyridone dyes

Abstract

This study examines electrooxidation behavior of three aryl azo pyridone using cyclic (CV) and square-wave voltammetry (SWV) on a glassy carbon electrode (GC) in Britton–Robinson (BR) aqueous buffer solutions and quantum-chemical calculations. Results indicate that the electrochemical activity is closely related to the presence of the hydrazone (–NH–N=) bridge of the dyes. The most stable protonated and deprotonated forms of dyes are identified by comparing experimental UV–Vis spectra with calculated spectra. Additionally, calculated ionization energies for both forms aligned with observed electrochemical activity, emphasizing the deprotonated anionic form as the most active. The proposed electrooxidation mechanism suggests that initial step involves dye deprotonation to achieve the most stable anionic form, followed by electron removal to generate a radical, and subsequent geometric adjustments to optimize electron density distribution and stability. The differences of the electrochemical behavior of dyes are discussed with consideration of underlying mechanism.