Combined spectroelectrochemical and theoretical study of a vinylene-bridged sexithiophene cooligomer: Analysis of the π-electron delocalization and of the electronic defects generated upon doping

The electronic and the Fourier transform Raman (FT-Raman) spectra of a novel well-barrier-well vinylene-bridged sexithiophene in neutral and in doped states have been recorded. The samples were oxidized chemically, with trifluoroacetic acid or ferric chloride, and electrochemically in dichloromethane solutions. The evolution of the Raman spectral pattern upon oxidation at different anodic potentials has been analyzed for a thin solid film of the material. Experimental observations are explained by the initial generation of a radical cation species followed by the generation of a dication species. A comprehensive assignment of the electronic and Raman spectroscopic features observed in both neutral and oxidized states has been performed on the basis of density functional theory (DFT) calculations. Time-dependent DFT calculations have been performed to calculate the electronic excitation energies. The experimental data and theoretical results give a clear picture of the structure and electronic properties of the charge defects created on this vinylene-bridged sexithiophene.