Conjugated bi- and terthiophenes have been substituted with cyano groups on several positions of the oligothiophene backbone. Their oxidation and reduction have been investigated in aprotic solvent (acetonitrile) by cyclic voltammetry. Most of the 10 studied compounds show two oxidation and two reduction waves, associated with the successive injection of one and two charges in these compounds. The reversibility of the first waves allows the determination of the formal potential of the corresponding radical cation, E(ox1), and radical anion, E(red1), and the calculation of an electrochemical energy gap, Delta E(g), = E(ox1) - E(red1). The energy gap and the oxidation potential are found to be primarily dependent on the conjugation length of the oligothiophene chain, and substituents allow a further fine-tuning of the energies of the occupied and unoccupied molecular orbitals.