CHARGED SOLITONS IN PERNIGRANILINE

The results of electron spin resonance measurements of the magnetic susceptibility are presented for polyaniline in the fully oxidized pernigraniline form; a conjugated polymer with a two-fold degenerate ground state. The magnetic susceptibility of pristine pernigraniline is extremely small, consistent with the proposed bond-alternated structure. After p-type doping to maximum levels (3-5 mol%), a very small increase in the spin concentration is observed. These susceptibility data are contrasted with the observed increase in conductivity (indicative of a relatively high density of charge carriers) and the appearance of a sub-gap absorption band. The results suggest that the dominant carriers and the charge storage species in acceptor-doped pernigraniline are charged solitons. In contrast, we found that p-type doping of the emeraldine base (where the ground state is non-degenerate) resulted in a major increase in the magnetic susceptibility, consistent with polarons becoming the dominant species.