Vibrational properties of polyaniline - Isotope effects

The effect of polyaniline deuteration on the Raman spectra of this polymer has been studied in detail. Four types of samples have been prepared: nondeuterated polyaniline, polyaniline deuterated selectively on the ring, polyaniline deuterated selectively on nitrogen, and polyaniline deuterated both on the ring and on the nitrogen. Selective deuteration allowed for experimental verification of the Raman modes assignment proposed for different types of polyaniline. In particular, the contribution of C-H bending to C-C stretchings in benzoid and quinoid rings of the polyaniline chain has been confirmed. In addition, selective deuteration enabled us to identify, for the first time in polyaniline, the band associated with N-H bending deformations. Raman spectroelectrochemical investigations of the four above-mentioned types of polyaniline samples gave evidence that in protonated polyemeraldine two types of structures coexist, namely, semiquinone radical cation (polaronic lattice) and quinoid dication (bipolaronic). The vibrations of the former are in resonance with the energy of the blue (457.9 nm) excitation line, whereas the vibrations of the latter undergo resonance enhancement if the red (676.4 nm) line is used. The calculated and experimentally observed Raman modes for both polaronic and bipolaron structures are in very good agreement in all four cases of differently deuterated polyaniline.