The optical transmittance spectra of polypyrrole perchlorate have been measured at various stages in the reduction to neutral polypyrrole at 300 and 120 K and at high pressure. Analysis of the results suggests that the polypyrrole chain is composed of conjugated segments of various lengths. The optical conductivity spectrum of polypyrrole perchlorate was obtained by the Kramers-Kronig transformation of the transmittance data from 0.025 to 6.25 eV. The spectrum is not consistent with Drude-Iike free carriers. The conduction mechanism probably involves hopping between the conjugated segments.

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The optical conductivity spectra of the conducting and insulating forms of the poly-β, β′-dimethylpyrrole perchlorate (PβDMP–ClO4) films have been determined by the Kramers–Kronig transformation of the transmittance spectra from 0.074 to 6.25 eV. The optical spectrum of the conducting form is not consistent with Drude-like free carriers. Absorption spectra have been measured on PβDMP-ClO4 films with various concentrations of perchlorate anions obtained using an electrochemical technique. Compared to those of polypyrrole perchlorate, the absorption spectra of PβDMP–ClO4 show some significant differences, especially in the low energy region of the almost neutral forms. Evolution of the PβDMP–ClO4 absorption spectra as a function of doping level is inconsistent with a rigid band model and is interpreted in terms of bipolaron formation on the chains.

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