Formation of singlet oxygen photosensitized by water-soluble metalloporphyrins

The quenching of the phosphorescence from complexes of Pt(II) and Pd(II) wi th three water-soluble porphyrins [meso-tetraksis(4-N,N,N-trimethylaminophe nyl)porphin, meso-tetraksis(4-N-methypyridyl)porphin, and meso-tetraksis(4- sulfonatophenyl)porphin] by molecular oxygen was studied. The quenching inv olves energy transfer and is accompanied by the formation of singlet oxygen . The quenching rate constants were determined; it was demonstrated that th eir values are close to the diffusion limit. The quantum yield of singlet o xygen formation was determined by a chemical method (with the RNO probe): P hi (Delta) = 0.1-0.9 for the different porphyrins. The quantum yield was de monstrated to be substantially influenced by the dimerization and aggregati on of the metalloporphyrins.