 | W. Fudickar, T. Linker
Why Triple Bonds Protect Acenes from Oxidation and Decomposition
J. Am. Chem. Soc. 2012, 134, 15071
DOI: 10.1021/ja306056x | | An experimental and computational study on
the impact of functional groups on the oxidation stability of
higher acenes is presented. We synthesized anthracenes,
tetracenes, and pentacenes with various substituents at the
periphery, identi
fi
ed their photooxygenation products, and
measured the kinetics. Furthermore, the products obtained
from thermolysis and the kinetics of the thermolysis are
investigated. Density functional theory is applied in order to
predict reaction energies, frontier molecular orbital inter-
actions, and radical stabilization energies. The combined results allow us to describe the mechanisms of the oxidations and the
subsequent thermolysis. We found that the alkynyl group not only enhances the oxidation stability of acenes but also protects the
resulting endoperoxides from thermal decomposition. Additionally, such substituents increase the regioselectivity of the
photooxygenation of tetracenes and pentacenes. For the
fi
rst time, we oxidized alkynylpentacenes by using chemically generated
singlet oxygen (
1
O
2
) without irradiation and identi
fi
ed a 6,13-endoperoxide as the sole regioisomer. The bimolecular rate
constant of this oxidation amounts to only 1
×
10
5
s
?
1
M
?
1
. This unexpectedly slow reaction is a result of a physical deactivation
of
1
O
2
. In contrast to unsubstituted or aryl-substituted acenes, photooxygenation of alkynyl-substituted acenes proceeds most
likely by a concerted mechanism, while the thermolysis is well explained by the formation of radical intermediates. Our results
should be important for the future design of oxidation stable acene-based semiconductors | | Zurück zur Übersicht » |
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