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 C60. The tetrapyrrolic metal binding sites in the diporphyrin arrays are either complexed to two ZnII or CuII ions, or, in a mixed coordination, to one CuII and one ZnII 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. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)