Charge-transporting properties of electropolymerized phenosafranin in aqueous media

The redox properties of polyphenosafranin were investigated at its different oxidation and protonation levels by potential scan voltammetry and electrochemical impedance spectroscopy. The polymer comprised phenosafranin units linked via a secondary amino nitrogen. A two-electron, two-proton process is proposed as its main redox reaction; its reduction yields the corresponding 5-hydro-phenazine form. In an isolated electroactive site, the polymer resembled redox polymers rather than conducting polymers. Low-frequency capacitance versus potential curves showed their maxima near the formal potential. Since the low-frequency capacitance increased linearly with the film thickness, it was identified with the redox capacitance. The width of the Warburg region showed a minimum at the half-reduced state of the polymer. This relationship indicated that electron transport was a key factor controlling the rate of charge transport in the polymer. The potential of the minimum Warburg width shifted to more negative values as the solution pH increased, with the minimum increasing exponentially with the pH. These observations lead to a conclusion that electron transport occurs via a process of sequential electron self-exchange between neighboring redox sites. This electron hopping is accompanied by proton transfer via intermolecular acid/base reactions.