SPECTROSCOPIC STUDIES OF ACCEPTOR AND DONOR DOPING OF POLYANILINE IN THE EMERALDINE BASE AND PERNIGRANILINE FORMS

Two methods of preparation of the neutral, fully oxidized form of polyaniline (pernigraniline) are presented, together with a comprehensive spectroscopic characterization of this alternating copolymer which has a two-fold degenerate ground sate. The IR spectrum is consistent with the pernigraniline structure; the UV-Vis spectrum of neutral pernigraniline consists of three bands at 2.2, 3.8 and 4.6 eV. The 2.2 eV absorption (band edge at about 1.8 eV) can be viewed as a transition from valence band to conduction band in the alternating copolymer. The 3.8 and 4.6 eV absorptions are attributed to π-π* transitions centered on the benzenoid and quinoid rings, respectively. We have investigated and compared the acceptor and donor doping of the partially oxidized emeraldine base and the fully oxidized pernigraniline. Iodine doping of pernigraniline leads to the appearance of a small shoulder near 1.5 eV in the electronic spectrum. Donor doping of both pernigraniline and emeraldine base leads preferentially to reduction of the quinoid rings. The acceptor doping of the emeraldine base proceeds on the benzenoid-amine sites. Possible self-localized excitations are proposed and discussed for these cases. © 1990.