1064-nanometer-excited Fourier transform Raman spectroscopy of conducting polymers

Application of 1064-nm-excited Fourier transform (FT)-Raman spectroscopy to the characterization of conducting polymers is described. 1064-nm-excited FT-Raman spectra with high signal-to-noise ratios are obtained from polyacetylene (PA), poly(1,4-phenylene) (PPP), poly(1,4-phenylene vinylene) (PPV) and poly(2,5-thienylene vinylene) (PTV) in their neutral (insulating) state. The resonant Raman spectra of acceptor- or donor-doped (conducting) PA and PPV are also obtained wih 1064-nm excitation. The resonant Raman spectra of Na-doped PA change in two stages with increasing dopant concentration, the first change corresponding to the increase in electrical conductivity and the second to the appearance of a Pauli susceptibility. The 1064-nm-excited FT-Raman spectrum of Na-doped PPV indicates existence of negative bipolarons which are equivalent to divalent anions extending over a few repeating units in the polymer chains.