Spectroelectrochemical Raman study of a novel well-barrier-well vinylene-bridged-octithiophene oligomer:: An analysis of the conjugation length and of the electronic defects created upon doping

We have studied the Fourier transform Raman (FT-Raman) spectra of a novel well-barrier-well vinylene-bridged-octithiophene in neutral and doped states. The compound was doped in a reaction with iodine vapors and electrochemically in the form of a thin film coated platinum electrode. We have analyzed the evolution of the Raman spectral pattern upon oxidation of the material at different anodic potentials. The data indicate that the oxidation process takes place in two well-differentiate steps: the initial formation of the radical cation followed by:the generation of the dication. The comparison of the spectroscopic data with those previously obtained on a related vinylene-bridged-quaterthiophene enabled us to draw conclusions about the effective pi -conjugation length in neutral state. RHF/3-21G* theoretical calculations have been performed to analyze the changes of the geometrical parameters when going from the neutral to the doped forms.