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Linear free energy relationship analysis of solvent effect on singlet oxygen reactions with mono and disubstituted anthracene derivatives
Ist Teil von
Journal of photochemistry and photobiology. A, Chemistry., 2009-09, Vol.207 (2), p.160-166
Ort / Verlag
Elsevier B.V
Erscheinungsjahr
2009
Link zum Volltext
Quelle
Elsevier ScienceDirect Journals Complete
Beschreibungen/Notizen
Detection of O
2(
1Δ
g) emission,
λ
max
=
1270
nm, following laser excitation and steady-state methods were employed to measure the total reaction rate constant,
k
T, and the reactive reaction rate constant,
k
R, for the reaction between singlet oxygen and seven mono and disubstituted anthracenes. In most solvents, the rate constants for the quenching of singlet oxygen by monosubstituted anthracenes are in the order of 10
6
M
−1
s
−1, whereas for the disubstituted compounds the values are in the order of 10
7
M
−1
s
−1 indicating that both, mono and disubstituted anthracenes are good quenchers of singlet oxygen. The reactive rate constants were very close to the total rate constants, implying that quenching is essentially a chemical process. The analysis of solvent effect on
k
T and
k
R by using LSER equations indicates that singlet oxygen deactivation by the anthracene derivatives is accelerated by solvents with large values of both, dipolarity/polarizability and Hildebrand solvent parameters, being inhibited by hydrogen bond donor solvents in some cases. Solvent effect analysis support the formation of a loose, zwitterionic like exciplex for 9-methylanthracene and 9-methoxyanthracene, a loose exciplex with partial charge separation for di-substitutes anthracene and a compact exciplex with partial charge separation for anthracene and 9-phenylanthracene.