Lower oxidation potentials than for the monomeric starting materials are displayed by the diporphyrins obtained by one-electron oxidation with tris(4-bromophenyl)ammonium hexachloroantimonate [see, for example, Eq. (1)]. This and the strong red shift observed for the Soret bands of the product are indicative of extensively delocalized pi-electron systems in the fused diporphyrin. Ar=3,5-di-tert-butylphenyl.