Theoretical and experimental investigation of absorption and Raman spectra of poly(paraphenylene vinylene)

We present experimental optical absorption and Raman data of poly(paraphenylene vinylene) (PPV) thermally converted at standard conditions at 300 °C. Theoretical calculations of the band shapes of both optical absorption and Raman spectra of standard PPV are reported, based on spectroscopic properties of known polymeric chains of different lengths. In particular, we have focused our study on the dependence of the Raman band intensities on the excitation wavelengths, taking into account the intensity changes observed in the Raman spectra of the oligomers. Such calculations are carried out by considering the electronic energies of optical transitions, the most intense Raman active vibrational frequencies, and the interactions between these vibrations and the electronic states of the oligomers considered. We show that the experimental data of optical absorption and Raman spectra can be theoretically accounted for, if a distribution of conjugated segments of different lengths is introduced in the evaluations.