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MECHANISM OF PHOTOREDUCTION OF THIAZINE DYES BY EDTA STUDIED BY FLASH PHOTOLYSIS‐II. pH DEPENDENCE OF ELECTRON ABSTRACTION RATE CONSTANT OF THE DYES IN THEIR TRIPLET STATE
Author(s) -
Bonneau Roland,
Violet Philippe Fornier de,
JoussotDubien Jacques
Publication year - 1974
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1974.tb06488.x
Subject(s) - flash photolysis , chemistry , thionine , protonation , photochemistry , reaction rate constant , triplet state , thiazine , reactivity (psychology) , methylene blue , aqueous solution , excited state , molecule , kinetics , medicinal chemistry , organic chemistry , photocatalysis , medicine , ion , physics , alternative medicine , electrode , quantum mechanics , pathology , nuclear physics , electrochemistry , catalysis
— 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.