Web Release Date: January 21,
Quenching of Singlet Oxygen by Oxygen- and Sulfur-Centered Radicals: Evidence for Energy Transfer to Peroxyl Radicals in Solution
and
Contribution from the Department of Chemistry, Iowa State University, Ames, Iowa 50011-3111, and Laboratoire D'électrochimie Organique et de Photochimie Redox, Universite of Joseph Fourier, B.P. 53-38041 Grenoble, Cedex, France
Received September 2, 1997
Abstract:
Quenching of singlet oxygen luminescence at 1.27 
m by
PhS
, PhSO, and peroxyl radicals
PhOO,
t-BuOO,
PhCH2OO,
Ph2CHOO, and
Ph3COO was studied in liquid solution.
The quantum yields of
decomposition of different initiators which lead to the formation of
free radicals were measured by using
nanosecond transient absorption. This allowed determination of
singlet oxygen O2(1
g)
quenching rate constants
by the radicals. They are <2 × 108
M-1 s-1 for the
sulfur-centered radicals and (2-7) × 109
M-1 s-1
for
peroxyl radicals in acetonitrile. The rapid quenching is
attributed to energy transfer quenching by the peroxyls,
which have an n 
* transition leading to a low-lying
2A' state above their 2A'' ground state.
PhSO is
shown computationally not to have such a low-lying 2A'
state. There may be a very low-lying 2B1
state, for
PhS, but it is apparently not an efficient acceptor of
electronic energy from
O2(1g).
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