Heterogeneous electron transfer (HET) from an aqueous redox couple, Ce(III):Ce(IV) to 2,2': 5',2"-terthiophene (3T) in 1,2-dichloroethane was investigated using potential-determining ions to establish an interfacial Galvani potential difference. The reaction was found to be potential dependent, and different thiophene oligomers species were identified spectroelectrochemically depending on the interfacial potential and the concentration of 3T present in the organic phase. At low concentrations, sexithiophene and its bipolaron were found to be the main products. At higher concentrations an insoluble black polymer was precipitated at the interface and sexithiophene radical cations and radical cation dimers were found to be present in solution.