The electrochemical synthesis of linear symmetrical octaethylporphyrin-octaethylporphyrin and unsymmetrical tetraphenylporphyrin-octaethylporphyrin dimeric porphyrins with one viologen as a spacer and of their precursor porphyrin monomers is reported. The mechanism of the electrochemical substitution leading to the dimeric porphyrins is discussed. These new compounds have been characterized by H-1 NMR, UV-vis spectroscopy, FAB mass spectroscopy, and microanalysis. Electrochemical data are reported, and the redox behavior is analyzed for the monomers and the dimers in terms of pi-pi interactions between the two porphyrin centers. ESR measurements were carried out on the unsymmetrical Cu-Zn and Cu-Cu dimeric metalloporphyrins which displayed intermolecular metal interactions.