Photoinduced Reactions of Porphyrin Photosensitizers A: Hematoporphyrin Derivative (HpD)
The excitation of HpD leads to the formation of singlet oxygen and radicals. Besides cytotoxic effects, photodestruction of the photosensitizer may occur. This process involves the decrease of the integral fluorescence (photobleaching) and the formation of photoproducts. Photoproducts from hematoporphyrin show a fluorescence around 640 nm in aqueous solution, a fluorescence decay time of about 2 ns and an additional absorption band around 640 nm, whilst photo-protoporphyrin has a fluorescence maximum at 670 nm with decay times around 1 and 5 ns and a pronounced absorption at 66S nm. The increased absorbance in the region of high tissue transmission is of interest for the photochemotherapy, however the photody-namic activity of the photoproducts is lower than that of hemato- and protoporphyrin as shown by hemolysis scattering experiments.
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