Differential multiwavelength Raman study of electrochemical redox transitions of polyaniline in solutions of different acidities.

A detailed Raman spectroelectrochemical study on polyaniline has been performed with the use of different laser lines ranging from UV (325 nm) through blue (442 nm) and green (532 nm) up to the red (633 nm) for spectra excitation, and within a broad range of solution pH from 1 to 9. From the data obtained, differential Raman spectra showing spectral changes occurring by a partial electrooxidation of polyaniline from its reduced to semioxidized, and by full oxidation to the fully oxidized states, were derived and analyzed. Different spectral features, appearing in electrochemical processes, were related to structural changes occurring during a partial or full electrooxidation of this polymer, to changes in its protonation state, and to resonance enhancement at different excitation wavelengths for different redox forms.