The infrared absorption and Raman scattering spectra recorded during the electrochemical oxidation of two sexithiophenes are reported. Using in situ spectroelectrochemical methods five oxidation states, neutral, radical cation, dication, radical trication, and tetracation of an alpha,alpha'-diphenyl sexithiophene, were studied. The experimental spectra are in agreement with the predictions of the effective conjugation coordinate theory and are in good accordance with theoretical density functional theory calculations.