Quantum yield of singlet oxygen production by monomeric and aggregated forms of hematoporphyrin derivative

Hematoporphyrin derivative (HpD) is a complex mixture of monoporphyrinic compounds, including hematoporphyrin, and oligomers containing up to eight porphyrin units. In methanol a sensitizer concentration-independent quantum yield of 0.64 is measured for the HpD-induced production of singlet molecular oxygen O-2 ((1)Delta (g)). This finding is consistent with the dye components remaining unassociated in this solvent. In water pH 7.4 HpD consists of a complex mixture of non-aggregated and self- and cross-aggregated monoporphyrinic and oligomeric species, and the quantum yield of O-2 ((1)Delta (g)) formation decreases significantly with increasing HpD concentration due to the lower quantum yield of aggregates. These variations can be quantitatively described in terms of a monomer-dimer equilibrium, with quantum yields of 0.64 and 0.11, respectively, for monomers and dimers. The yields of unassociated species are identical in methanol and water. (C) 2001 Elsevier Science Inc.