Vibrational spectroscopic study of a series of α,α′-diethyl end-capped oligothiophenes with different chain lengths in the neutral state

In this paper, we investigate the vibrational FT-LR and FT-Raman spectra of a series of alpha,alpha'-diethyl substituted oligothiophenes with variable chain lengths (from trimer to hexamer) in the neutral state. The experimental data support the existence of an effective intramolecular delocalization of the pi electrons. Ab initio quadratic force field calculations, at the RHF/6-31G** level, have been carried out for each oligomer, with the chain length dependence of the Raman spectra being simulated with remarkable accuracy.