Vibrational spectroscopic study of a series of alpha,alpha '-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 experimen tal data support the existence of an effective intramolecular delocalizatio n 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 acc uracy.