Evidence for the Polaron State in Polyaniline from in situ Electron Spin Resonance and Resonance Raman Spectroscopy

A combined investigation of the Raman cross-section for a benzene ring vibrational mode at 1630 cm −1 and of the spin concentration as a function of the e.c. potential in polyaniline identified the polaron state as the initially generated doping-induced species. The polaron transition energy is determined as 2.75 eV. Increasing oxidation quenches the Raman signal and decreases the spin concentration until, for oxidation potentials higher than 700 mV vs . SCE, both signals reappear indicating a reduction of the polaron lattice or of bipolaron states to individual polarons.