A new approach for the electrochemical characterization of water-insoluble azo dyes

• Water-insoluble azo dyes investigated in non-electrolytic media for the first time • A novel charging–discharging approach is proposed for evaluation of first oxidation event • HOMO-LUMO of the dyes determined from the experimental spectral and DPV data • Ground-state equilibrium geometries of the dyes obtained by B3LYP/6-311++G** in DMSO We present a novel approach for investigating water-insoluble dyes through the controlled charge/discharge of dye molecules. This method serves as an alternative means of registering the initial oxidation event required for the HOMO-LUMO transition in non-conductive media. Four dyes Methyl Red, Methyl Yellow, Sudan Black, and 1-(2-Pyridylazo)-2-naphthol were dissolved in DMSO and analyzed to determine their electrochemical oxidation and reduction potentials toward their broader applicability. In addition to calculating HOMO-LUMO energy levels from experimental data (UV-Vis spectroscopy and differential pulse voltammetry), we report, for the first time, the boundary orbital energies and ground-state equilibrium geometries of these dyes obtained by quantum chemical calculations at the B3LYP/6-311++G** theoretical level. The experimental and theoretical results are compared and discussed.