Raman resonances in sulfonate or Cl--doped PANI films

The Raman spectra of polyaniline (PANI) doped by functionalized sulfonic acids present very few differences with the spectra obtained after doping by inorganic anions, in spite of the noticeable differences displayed elsewhere by their optical spectra: the 3 eV (localized polaron) as well as 1.5 eV bands are stronger and sharper in presence of sulfonate. In fact, during the study of the different PANI forms. it was observed that the connections between Raman and optical features are far from being straight; a simple analysis in terms of resonance in either benzoid or quinoid units is not enough. To arrive to a better understanding of these connections, we have compared the Raman spectra obtained with blue (localized polaron excitation), red (excitonic resonance) and near-IR (intrachain excitations resonance) lines; with the green laser line, PAM is out of resonance. Spectra were also obtained on samples treated to present a "secondary doping", and therefore a strong IR absorption. The use of red and IR lights allows to study the splitting of the C=N peak, which can clearly be decomposed in two sub-bands, as well as the splitting of the 1330 cm(-1) peak (assumed to be due to the stretching of C - N+.).