Proton‐Dependent Electrochemical Behavior of Oligomeric Polyaniline Compounds

The redox chemistry of a model compound of polyaniline, N,N'‐diphenyl‐p‐phenylenediamine, has been studied in acidic media. The redox processes of this "dimer" have been shown to be highly reversible and p H‐dependent. The dimer undergoes a two‐step oxidation from amine to radical cation to imine forms. An equilibrium constant was determined for the conversion of a 50:50 mixture of amine and imine forms to the radical cation as a function of proton concentration. A 50% conversion to the radical form occurs at a p H of 2.2. This p H value corresponds very well with the midpoint of the metal‐to‐insulator transition in polyaniline as a function of p H. ESR measurements were used to study the radical cation in solution. Spin density was found to be highest on the nitrogens, but considerable delocalization into central and end phenyls was found.