KINETIC ESR STUDIES OF THE REACTIONS BETW EEN EXCITED PHOTOSENSITIZERS AND STABLE FREE-RADICALS

Decrease in the concentration of the stable free radical 4,4'-di-tert. -butyl-diphenyl-1-nitroxyde in the presence of the photosensitizer mes o-tetrahydroxy-phenyl-chlorin has been followed by kinetic electron sp in resonance spectroscopy during illumination by light above 610 nm in deoxygenated environment. Kinetic calculations yielded the rate const ant of the direct interactions between triplet sensitizer molecules an d doublet stable free radicals. By adding to the system the spin trap alpha-(4-pyridyl-1-oxide)-N-tert.-butyl-nitrone, the rate of the loss of paramagnetism decreased due to the elimination of free radicals ste mming from the excited sensitizer, proceeding via electron transfer an d being similar to 8 . 10(7) 1 mol(-1) s(-1)