DYNAMICS OF POLYTHIOPHENE WITH DEFECTS

New infra-red and Raman experiments on undoped and doped polythiophene films, obtained in various synthesis conditions, are reported. The samples present a broad distribution of conjugation length. To explain all the observed spectra we develop a discrete force field model. Then, using this model and a new powerful computing process, the spectral moments method, we have been able to interpret practically all principal features observed: not only are the calculated frequencies very close to the experimental data but the intensities and the behaviour with conjugation length of the infra-red and Raman lines are in fair agreement for undoped and doped polythiophene. In particular, in infra-red, the emergence upon doping of four intense lines at 1032, 1117, 1203 and 1334 cm-1, and other features less intense, and in isotropic Raman scattering the reduction of the intensity of all lines, are nicely reproduced. Taking into account our previous results obtained for the perfect chain it is possible to furnish a reasonable interpretation of the infra-red and Raman spectra of the polythiophene. In particular, the infra-red activity is very well represented with a simple tensor charge model without explicitly taking into account the fluctuation of the charge density.