Vibrational spectra of charged defects in a series of alpha,alpha '-dimethyl end-capped oligothiophenes induced by chemical doping with iodine

We present the results of a detailed study carried out on a few alpha,alpha '-dimethyl end-capped oligothiophenes which have been in situ doped with dr y iodine vapors, at different concentrations. The doping process of these w ell sized oligomers (from dimer to hexamer) has been monitored by using Fou rier transform infrared absorption and Fourier transform raman scattering s pectroscopies. These data, when combined with the vibrational full assignme nt of the oligomers in the neutral state and the electronic absorption band s recorded for both neutral and doped compounds, provide a complete spectro scopic characterization of a full series of positive polaron-type model def ects of doped polythiophene. We have also performed density functional theo ry quantum-chemical calculations in order to analyze the effects of ionizat ion on the geometries and vibrational spectra of these systems. (C) 1998 Am erican Institute of Physics. [S0021-9606 (98)70347-2].