Vibrational study of a well–barrier–well thiophene–based oligomer in relation to the effective π-conjugation length

We have studied the Fourier transform infrared (FTIR) and the Fourier transform Raman (FT-Raman) spectra of a new thiophene-based oligomer in neutral form. The compound has a well–barrier–well structure, where the well parts are two bithienyl end moieties and the barrier part is a vinylene fragment with a larger energy gap. Characteristic features are correlated with vibrational data of unsubstituted α-linked oligothiophenes and α,α′-dimethyl end-capped oligothiophenes to assess information about the effective conjugation length of this oligomer. The FTIR and FT-Raman spectra have also been theoretically calculated at the B3LYP/6-31G** and RHF/6-31G** levels, respectively, to propose a vibrational assignment for the main bands in the whole spectral range.