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SENSITIZED PHOTOOXYGENATION ACCORDING TO TYPE I MECHANISM (RADICAL MECHANISM) ‐ PART I. FLASH PHOTOLYSIS EXPERIMENTS
Author(s) -
KRAMER H. E. A.,
MAUTE A.
Publication year - 1972
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.1751-1097.1972.tb06218.x
Subject(s) - photooxygenation , thionine , chemistry , flash photolysis , singlet oxygen , photochemistry , oxygen , radical , photobleaching , aqueous solution , redox , inorganic chemistry , electrochemistry , reaction rate constant , kinetics , organic chemistry , fluorescence , physics , electrode , quantum mechanics
— The photooxygenation of allylthiourea (ATU) sensitized by thionine does not occur according to the singlet oxygen mechanism but rather proceeds via the formation of radicals. In oxygen‐free solution the primary process is a redox reaction between the thionine triplet and ATU where a semithionine‐ and an ATU‐radical are formed. In further reaction steps the leuco form of the dye is finally produced (reductive photobleaching; D R mechanism after Koizumi). The primary process in an oxygen‐containing aqueous solution is the same, since at high concentrations of ATU (0·2 M ) the amount of semithionine formed by a photolytic flash, as well as the time course of disappearance of semithionine, does not depend on the oxygen content of the solution. The reformation of thionine following flash photolysis has been investigated with regard to oxygen concentration and pH dependence. Two different excitation intensities were used. A quadratic dependence of thionine reformation on excitation intensity at high oxygen concentration was observed, indicating a reaction between two photoproducts. The dependence of the reaction rate of semithionine on the ionic strength has been investigated. These experiments show that the reaction partner of semithionine carries a charge of + 1 in oxygen‐free as well as in oxygen‐saturated solution.