EXPERIMENTAL AND THEORETICAL-STUDY OF VIBRATIONAL PROPERTIES OF POLYTHIOPHENE, POLYMETHYLTHIOPHENE AND POLYOCTYLTHIOPHENE

We report spectroscopic studies (RRS and FTIR) of some thiophene oligomers, polythiophene and polyalkylthiophenes. The polymers have been synthetized from thiophene, 2.2'-bithiophene, methylthiophene and octhylthiophene respectively. The vibrational results are interpreted by dynamical calculations based on a valence force field model. A complete set of force constants is obtained and compared to those found in other compounds (1). These calculations provide a better understanding of the vibrational properties. Particulary, the Raman modes at 1498, 1365 and 700 cm-1 in polythiophene are completely assigned. In order to understanding the conducting properties of these polymers, we have doped polythiophene and we propose an interpretation of the new spectrum, in terms of changes occurring in the determination of some force constants.