meso,meso-linked and triply fused diporphyrins with mixed-metal ions:: Synthesis and electrochemical investigations

A novel series of biaryl-type, meso,meso-linked and planar, triply fused diporphyrin derivatives was prepared and fully characterized together with the corresponding monoporphyrin control compounds. They feature peripheral meso-3-cyanophenyl and meso-3,5-cyanophenyl groups, which have previously been shown to undergo transformation into malonates without perturbation of the porphyrin core and subsequent Bingel addition to fullerene C-60. The tetrapyrrolic metal binding sites in the diporphyrin arrays are either complexed to two Zn-II or Cu-II ions, or, in a mixed coordination, to one Cu-II and one Zn-II ion; alternatively, one or both sites remain unoccupied. The interaction between the differentially metallated porphyrin rings was systematically investigated by UV/Vis spectroscopy and electrochemistry. Cyclic voltammetry and differential pulse voltammetry reveal that electronic communication in the diporphyrin arrays varies strongly with the mode of connection (meso,meso-linked or triply fused), the nature of the bound metal ion, and the number of peripheral cyano groups. The electrochemical HOMO-LUMO gap in both series of diporphyrins is strongly but differentially affected by the choice of the inserted metal ions. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).