Abstract The singlet oxygen quantum yield of photodynamic agents was measured at 546 nm, 630 nm, and on the far-red absorption peak. The technique employed is available in most laboratories, in which the photosensitization of lysozyme is used as an internal actinometer. Measurements in a pH 7.4 phosphate buffer plus 1% Triton X-! 00 (PB/X 100) are scaled to 0.52 for methylene blue in the phosphate buffer. The average quantum yields are: hematoporphyrin IX (0.73), protoporphyrin IX (0.56) zinc protoporphyrin IX (0.91), mesotetra-(4-sulfonato-phenyl) porphine (0.61), Photofrin s (0.89), benzoporphyrin derivative monoacid ring-A (0.84), chlorin e6 in PB (0.64), pheophorbide a (0.69), and aluminum phthalocyanine tetrasulfonate (0.38). Protection factors were measured for added azide ion, 1,4-diazabicyclo [ 2.2.2]-octane, and superoxide dismutase. Spectral evidence is presented for chlorin e6 interactions with PB/TX 100 and for binding to lysozyme
