Protoporphyrin IX and hematoporphyrin derivatives interactions with oxygen studied by time and spectral resolved phosphorescence

In this contribution energy transfer from chemically similar porphyrin-like molecules of hematoporphyrin derivatives and protoporphyrin IX, used in photodynamic therapy as photosensitizers was investigated. The photosensitizers phosphorescence (about 840 nm) kinetics together with singlet oxygen production were measured by means of IR time and spectral resolved phosphorescence (at 1275 nm) in wide range of the photosensitizer concentrations (5–200 μM). The submicrosecond photosensitizers triplet life-times were compared to submicrosecond singlet oxygen phosphorescence rise-times. Moreover, microsecond singlet oxygen phosphorescence life-times and rate constants of singlet oxygen quenching by the photosensitizers were determined. The differences in obtained life-times and concentration trends were discussed and explained in the frame of the photosensitizers aggregation. Hematoporphyrin derivatives behave as non-aggregating photosensitizer, while protoporphyrin IX exhibits an aggregation.