Spectroelectrochemical investigations of the mechanism of the electro-oxidation of 3,3′-dimethylnaphthidine

The mechanism of the electrode oxidation of 3,3′-dimethylnaphthidine (DMN) was studied on Pt electrodes and optically transparent n-SnO₂ electrodes (n-SnO₂ OTE). DMN undergoes a one-step reversible two-electron electrode reaction. Spectroelectrochemical and EPR investigations revealed the presence of free radicals in the electrolysed acetonitrile solution of DMN, as well as in the solid-state product of the electrode reaction. Spectroelectrochemical measurements together with computer simulation show that the reaction follows an EC mechanism, the product being a biradical dication (DMN^β2+) which absorbs radiation at λ=510 nm. It undergoes rapid reversible reactions with the water present in acetonitrile, yielding 4,4′-diiminedinaphtha-3,3′-dimethyl-1,1′-quinone, which absorbs radiation at λ = 550 nm.