Non-covalent cofacial heterodimers and -trimers between meso-tetraphenyl-octacarboxylate-porphyrin and beta -tetracationic porphyrins have been prepared in bulk water. They are held together by Coulomb interactions between four or eight beta -methylpyridinium and meso-phenylcarboxylate ion pairs. The observation of the UV-vis absorption titration indicated quantitative trimerization at concentrations >10(-6) M. The equilibrium constants in water were 2.3 x 10(6) M-1 for the dimerization and 1.7 x 10(7) M-1 for the conversion of the dimer to the trimer in water. Fluorescence of free base or zinc porphyrins was strongly diminished on heterodimerization and -trimerization by redox quenching. In the case of Mn(III) heterotrimer, electrochemistry and spectroelectrochemistry showed that all three Mn(III) ions were oxidized simultaneously to Mn(IV) at a potential close to 0.20 V versus Ag \ AgCl at pH 12. Electroreduction of the peripheral cationic Mn(III) porphyrins was achieved at - 0.20 V versus Ag \ AgCl and gave the first multivalent trimers, namely Mn(II)P-Mn(III)P-Mn(II)P. The reduction of the central manganese porphyrin finally occurred at -0.60 V yielding Mn(II)P-Mn(II)P-Mn(II)P trimers. Heterotrimers Mn(III)P-H2P-Mn(III)P and H2P-Mn(III)P-H2P were also studied as reference compounds for electrochemical measurements.