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MECHANISM OF PHYSICAL QUENCHING OF SINGLET MOLECULAR OXYGEN BY CHLOROPHYLLS and RELATED COMPOUNDS OF BIOLOGICAL INTEREST
Author(s) -
Tanielian C.,
Wolff C.
Publication year - 1988
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.1751-1097.1988.tb02821.x
Subject(s) - chemistry , photochemistry , quenching (fluorescence) , singlet oxygen , tetraphenylporphyrin , intersystem crossing , triplet state , excimer , oxygen , benzene , singlet state , porphyrin , molecule , fluorescence , organic chemistry , excited state , physics , quantum mechanics , nuclear physics
— The rate constant k 5 / > for physical quenching of singlet oxygen O 2 (δ 1 ;) by the sensitizer in dye‐sensitized photooxygenations is determined in the case of chlorophylls a and b (7.3 times 10 8 , 4.2 times 10 8 M ‐1 s ‐1 respectively), pheophytins a and b (7.4 times 10 7 , 3.0 times 10 7 M ‐1 s _1 respectively), tetraphenylporphyrin (4.4 times 10 7 M ‐1 s _1 ), magnesium tetraphenylporphyrin (5.0 times 10 8 M ‐1 s _1 ), zinc tetraphenylporphyrin (1.5 times 10 8 M ‐1 s _l ) and protoporphyrin IX‐dimethylester (9.1 times 10 7 M ‐1 s _1 ) in benzene. These sensitizers show a linear correlation between log k s O , and their half‐wave oxidation potentials and the value of the slope is similar to that observed for various compounds such as phenols. It is concluded that (i) the interaction between chlorophylls and related compounds with singlet oxygen may involve an exciplex as for phenols, and (ii) physical quenching may be envisaged as a spin‐orbit‐induced intersystem crossing within the exciplex.