Reversible dimerization of the anion radicals of some dicyanonaphthalenes

► Study of seven isomers of dicyanonaphthalene reveals two new cases of reversible dimerization. ► Weak dimerization can be detected from the shape of the voltammogram. ► Systems with larger dimerization equilibrium constants show a separate oxidation peak for the σ-dimer. ► Dimerization equilibrium constants correlate with spin density at the site of dimerization.