MECHANISM OF PHYSICAL QUENCHING OF SINGLET MOLECULAR OXYGEN BY CHLOROPHYLLS and RELATED COMPOUNDS OF BIOLOGICAL INTEREST
- 1 September 1988
- journal article
- research article
- Published by Wiley in Photochemistry and Photobiology
- Vol. 48 (3) , 277-280
- https://doi.org/10.1111/j.1751-1097.1988.tb02821.x
Abstract
Abstract— The rate constant k5/ > for physical quenching of singlet oxygen O2(δ1;) by the sensitizer in dye‐sensitized photooxygenations is determined in the case of chlorophylls a and b (7.3 times 108, 4.2 times 108 M‐1 s‐1 respectively), pheophytins a and b (7.4 times 107, 3.0 times 107M‐1 s_1 respectively), tetraphenylporphyrin (4.4 times 107 M‐1 s_1), magnesium tetraphenylporphyrin (5.0 times 108M‐1 s_1), zinc tetraphenylporphyrin (1.5 times 108 M‐1 s_l) and protoporphyrin IX‐dimethylester (9.1 times 107M‐1 s_1) in benzene. These sensitizers show a linear correlation between log ksO, 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.This publication has 27 references indexed in Scilit:
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