Nature of protons, phase transitions, and dynamic disorder in poly- and oligoaniline bases and salts: An inelastic neutron scattering study

An inelastic neutron scattering study of polyaniline (camphorsulfonic and chloride salts, emeraldine base in the form of powder or film) from ca. 1 to 120 cm(-1) shows significant changes in the compounds as a function of the temperature. Intensity and bandwidth undergo major modifications below 50 K, because of the freezing of the dynamic ring disorder. The greatest modifications were observed for camphorsulfonic acid salt. In the range from 100 to 3000 cm(-1), a nonlocalized inelastic scattering process previously assigned to the "free protons" (in other words, noncovalently bonded hydrogen atoms) was also observed. Comparison with the spectra of oxidized tetramer (BQBBa), BB (diphenylamine), BBB (N,N'-diphenyl-1,4-phenylenediamine), and BQB (-diimine) model compounds shows that, at the neutron spectrometer resolution, the dynamics of BQB already give a good basis for the aromatic ring dynamics in a polyaniline framework. Assignment of the modes is proposed in the light of low-wavenumber Raman and IR spectra. The thermal disordering of the rotational degrees of freedom appears very similar to that observed in crystalline benzene.