Substituent effects of the para substituent X were found to be small, but as expected, with the potentials varying as H > Me > OMe. Given the focus of the present study, we have not, as of yet, attempted to understand the origin of the irreversibility of the first oxidation wave. Equating the difference between the first oxidation peak potential and the reduction potential to the electrochemical HOMO-LUMO gap, we arrive at a narrow range of values, 1.97 ± 0.05 V vs.