The dimerization of meso-tetrakis(4-sulfophenyl)porphyrin (TPPS) in aqueous solution was studied by electrochem. methods. In weak acidic solution, TPPS dimerizes easily and its characteristic peaks can be seen in either visible absorption spectra or cyclic voltammogram. With the known dissociation constants K3, K4 and the dimerization formation constant KD of TPPS the amount of dimer at different pH was calculated, and it reaches its max. at about pH 5. This result agrees with the experimental data in HOAc-NaOAc. Then the model of the dimer is proposed as H3P+-H2O-H3P+, i.e., 2 monomers are linked together by the hydrogen bond between TPPS and H2O. The factors influencing the formation of the dimer, including the TPPS concentration, the pH value of the solution, the formation of metal complexes, etc., were studied and explained.

Key words: AQUEOUS SOLUTION, DIMER, ADSORPTION, CHELATION REACTION, CYCLOVOLTAMGRAPH, PORPHYRIN, OXIDATION-REDUCTION POTENTIAL, FUEL CELL