Vibrational study of the FeCl3-doped dimer of polyaniline; A good model compound of emeraldine salt

In this paper, optical and vibrational properties of the FeCl3-doped dimer of polyaniline, a model compound of emeraldine salt are presented. This oli gomer is synthesized according to the method reported by Zaghal et al.. A c omplete assignment of the fundamental in-plane Raman and infrared modes (17 00-600 cm(-1)) of this oligoaniline is proposed. The observed frequencies o f the dark blue microcrystals are compared with those acquired by vibration al calculations based on a valence force field model. To show, by a most ef ficient way, the evolution of the electronic configuration of the dimer upo n doping, the experimental vibrational modes of the doped dimer and its rel ated force constants are compared with those of its fully reduced and oxidi zed forms. The strongly aromatic and semiquinone-like characters of the rin gs present in the doped dimer is put in evidence by Resonance Raman Scatter ing and infrared absorption and confirmed by vibrational calculations. Cons idering the numerous similarities between the vibrational characteristics o f the polymeric chain and its well-defined oligomer, this study also provid es useful information about the electronic configuration of the protonated emeraldine, which remains under debate.