Ab initio HF and DFT calculations of geometric structures and vibrational spectra of electrically conducting doped oligothiophenes

This article reports results of a theoretical study of the effect of ioniza tion on the infrared spectra of a series of alpha,alpha'-dimethyl end-cappe d oligothiophenes with the purpose of obtaining a theoretical insight into the geometry and spectral changes occurring on doping polythiophene. For th at purpose we determined the structures, vibrational frequencies and infrar ed intensities of the neutral oligomers, their radical cations and their di cations. Ab initio HF and DFT molecular orbital calculations were employed to assess the structural and spectral changes from neutral to charged state s. (C) 1999 Elsevier Science B.V. All rights reserved.