In this work, we have used an oligomer model compound approach for the understanding of the vibrational spectra of the principal forms of polyaniline. Selected model compounds have been studied by Raman and infrared (IR) spectroscopies. The observed vibrational bands are assigned to the expected modes, by revealing the relationships between molecules. In a more theoretical part, dynamical calculations on the different model compounds and their related polymers are presented. The use of model compounds allows us to reach better sets of force constants, as soon as we assume that the parameters can be transferred to the polymeric forms. The obtained values of these force constants are discussed in regards to the oxidation state of polyaniline and its corresponding geometrical structure.

In this paper, optical and vibrational properties of the FeCl 3 -doped dimer of polyaniline, a model compound of emeraldine salt are presented. This oligomer is synthesized according to the method reported by Zaghal et al.. A complete assignment of the fundamental in-plane Raman and infrared modes (1700-600 cm -1 ) of this oligoaniline is proposed. The observed frequencies of the dark blue microcrystals are compared with those acquired by vibrational calculations based on a valence force field model. To show, by a most efficient way, the evolution of the electronic configuration of the dimer upon doping, the experimental vibrational modes of the doped dimer and its related force constants are compared with those of its fully reduced and oxidized forms. The strongly aromatic and semiquinone-like characters of the rings present in the doped dimer is put in evidence by Resonance Raman Scattering and infrared absorption and confirmed by vibrational calculations. Considering the numerous similarities between the vibrational characteristics of the polymeric chain and its well-defined oligomer, this study also provides useful information about the electronic configuration of the protonated emeraldine, which remains under debate.

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Experimental and theoretical studies of basic forms of polyaniline are presented. Experimental spectra of emeraldine, leucoemeraldine and pernigraniline and their oligomer model compounds (diphenylamine, phenyl‐end‐capped dimer, phenyl‐end‐capped tetramer, phenyl‐end‐capped hexamer, imine form of phenyl‐end‐capped dimer, pernigraniline base phenyl‐end‐capped tetramer and emeraldine base phenyl‐end‐capped tetramer) were recorded in N‐methyl‐2‐pyrrolidone solution and in the solid state. The calculations were performed using the valence force field model. A non‐planar geometry of the polymers studied was taken into consideration and particular phenylene ring torsions rendering the system non‐planar were analyzed. The assignments of the observed modes was made possible by comparison of the calculated and experimentally measured wavenumbers. Copyright © 2000 John Wiley & Sons, Ltd.

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