Study of redox and protonation processes of polyaniline by the differential multiwavelength Raman spectroelectrochemistry.

Polyaniline layer has been deposited at a gold electrode and subjected to differential multiwavelength Raman spectroelectrochemical study. A broad set of laser line excitation wavelengths was used, including UV (325 nm), blue (442 nm), green (532 nm), red (633 nm), and far red (785 nm). From measurements performed, potential-difference Raman spectra, related to small-step changes of electrode potential were derived, and specific spectral and structural features were obtained and analysed. Similarly, pH-difference spectra for solution pH changes were obtained. A strong resonance enhancement of Raman spectra for reduced form of polyaniline at UV and blue line excitations, and for oxidized forms at red and far red excitations was observed and analysed. The 442-nm excited potential-difference resonance Raman spectra revealed presence of intermediate oxidation state compound formed during the electrooxidation of leucoemeraldine with characteristic vibrational bands at 1622, 1187, 881, and 817 cm-1.