Characterization of magnesium porphyrins and aggregation of porphyrins in organic solvent

Magnesium tetrakis(4-sulfonatophenyl)porphyrin complex was synthesized and purified. MgTPPS (tetrasodium salt) and MgTPPSC8 (tetraoctylammonium salt) showed unique spectroscopic behaviors in an aqueous buffer and CH3OH respectively, indicating solvent ligation on the Mg ion. In pure CH2Cl2, the MgTPPSC8 formed unique J-type oligomers, in which the sulfonato groups mutually coordinate to the vicinal Mg ion. In binary solvent systems of CH2Cl2 and CH3OH, MgTPPSC8 formed H-aggregates as well as other TPPS derivatives, and aggregation was controlled by changing the ratio of the solvents. The geometrical structure of J-type oligomers was estimated by using the exciton point-dipole coupling theory.