Such species with a -bond should have a much lower HOMO level, leading to an anodic shift of the oxidation potential, however, it is not the case. DFT calculations also suggest that the most stable structure is the open-shell species 2 •• , and thus, the -bonded species can be excluded in the later discussion. The differences in reduction potentials among the three dications 2 2+ with different substituents are small (~0.2 V) for both E 1 red and E 2 red /V, suggesting that the coefficients of LUMO of 2 2+ are mainly located on the xanthylium units. Furthermore, a twisted geometry of the aryl group to the xanthylium unit also suppresses effective conjugation. Thus, the donating ability of aryl groups does not affect the reduction potentials.