Polypyrrole is an electrochemically synthesized conductive polymer that has physical properties which impede efforts to develop structure-properties relationships. The extent of conjugation, as limited by the presence of structural disorders in the polymer, is important in determining its inherent conductivity. The extent of conjugation in thin electrochemically generated films of polypyrrole and poly-N-methylpyrrole has been examined with resonance Raman spectroscopy. The Raman experiment was performed within the electrochemical cell and does not suffer from exposure to the contaminants encountered when transfer techniques are employed.

Electrochemically reduced films of polypyrrole exhibited intense resonance Raman spectra of the carbon-carbon stretching frequencies. The position of these bands is a function of the number of double bonds in conjugation. The conjugation length within the polymer chain was found to be between 3 and 4 rings for PP and slightly less in PNMP (2-3 rings). This is the first reported determination of the conjugation length in PP and PNMP. This data confirms the idea that PNMP is less conductive than PP due to reduced planarity within the chain, thus less conjugation.

Reduced films of PP and PNMP yielded intense luminescence that disappeared upon oxidation. The luminescence is a broad featureless band that consumes the weakly enhanced Raman of PNMP. The intensity of the luminescence increased as the reduction potential increased and the highest intensities occurred at potentials far cathodic of the E₀ for the film. The explanation for this is still obscure but may involve either further reduction of highly luminescent segments or a decrease in the amount of quenching by solvent or counter-ion interactions with the luminescer.