The determination of the redox potentials of the radical species of a conductive polymer with a spectroelectrochemical technique

The electrochemical and spectroelectrochemical properties of poly-(3,4-propylene-dioxythiophene-heptyl2) (PProDOT-heptyl2) film was studied by cyclic voltammetry, in situ UV–Visible spectroscopy, and in situ conductivity measurement. The cyclic voltammograms recorded for PProDOT-heptyl2 revealed redox peaks at 0.32/0.23 V. The in situ conductivity of PProDOT-heptyl2 was measured at various potentials from −0.4 V to +0.75 V and found to be 0.19 S/cm at +0.4 V. Spectroelectrochemical experiments were performed to observe the absorption bands of the PProDOT-heptyl2 film in the neutral and oxidized forms. The derivative cyclic voltabsorptometric (DCVA) curves obtained for the PProDOT-heptyl2 film illustrated the presence of neutral, polaron, and bipolaron states. The absorption band of the polymer at 520 nm is assigned due to the π–π∗ electronic transition of the film in the neutral state. The redox potentials of the polaron and bipolaron states were determined by DCVA to be +0.27 V and +0.69 V, respectively, which corresponds to the absorption bands of polaron at 760 nm and of bipolaron at 710 nm.