Photochemistry and Photobiology · 1974 · 45 citations · 10 references
Natural SciencesBiochemistryChemistryChemical KineticsInorganic ChemistrySpectroscopyPhotocatalysisPhotochemical KineticsPhotochemistryPhotosystem IiExcited-state ReactivityOrganic Dye PhotophysicsPh DependencePhotochemical Reaction KineticsRate Constant DeterminationTriplet State ChemistryTriplet State PhotochemistryTriplet States
Abstract— The pH dependence of the apparent reactivity of thiazine dyes in their triplet states has been studied in aqueous solutions, using as electron donor HY ‐3 , the trianionic species of ethylene diamine tetraacetic acid (EDTA), in the pH range 4–8. The pH dependence is found to be related to a change in the degree of protonation of the triplet excited dye. The apparent reactivity and lifetime of two differently protonated forms of thionine, azur B and methylene blue were determined by classical and dye‐laser flash techniques, making it possible to evaluate the rate constant for electron abstraction of these molecules in their triplet states. It is found that: (a) protonation on the ring nitrogen increases the electron‐abstraction rate constant of the triplet‐state species about twenty‐fold, and (b) methylation on the side amino groups decreases it.
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