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

Hematoporphyrin derivative (HpD) is a complex mixture of monoporphyrinic co mpounds, including hematoporphyrin, and oligomers containing up to eight po rphyrin units. In methanol a sensitizer concentration-independent quantum y ield of 0.64 is measured for the HpD-induced production of singlet molecula r oxygen O-2 ((1)Delta (g)). This finding is consistent with the dye compon ents remaining unassociated in this solvent. In water pH 7.4 HpD consists o f a complex mixture of non-aggregated and self- and cross-aggregated monopo rphyrinic 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 quantitat ively described in terms of a monomer-dimer equilibrium, with quantum yield s of 0.64 and 0.11, respectively, for monomers and dimers. The yields of un associated species are identical in methanol and water. (C) 2001 Elsevier S cience Inc.