‘In situ’ spectroelectrochemical study of a series of α,α′-dimethyl end-capped oligothiophene films

The electrooxidation of α,α′-coupled thiophene oligomers alkyl-protected toward anodic coupling at the terminal α positions was studied in solid state at room temperature. Reversible oxidation goes from a single one-electron step oxidation for the tetramers to two separate one-electron steps for the pentamer and hexamer. The oxidation potentials are found to be primarily dependent on the conjugation length of the oligothiophene chain. The ‘in situ’ visible spectra of the electrochemically prepared oxidation states have also been investigated. A model based on the formation of charged molecular associates such as π-dimers or π-stacks successfully explains the spectroscopic results.