The nature of the charge carriers in conducting polypyrrole highly doped with p-toluenesulphonate and their behavior under pressure was investigated by high-pressure Raman spectroscopy. Changes of band positions and relative intensities of bands assigned to the radical cation (polaron) or the dication (bipolaron) were observed. The results are discussed in the context of structural and electronic aspects by comparing the pressure effects with those observed in the Raman spectrum obtained from oxidized or reduced samples. The changes of the relative number of both charge-carrier species indicated in the Raman spectra under pressure are explained by a shift in the character of the dominant charge carriers from bipolarons to polarons.

• Received 13 August 2001

DOI:https://doi.org/10.1103/PhysRevB.65.174202