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Oxygen Quenching of n π * Triplet Phenyl Ketones: Local Excitation and Local Deactivation
Author(s) -
Schweitzer Claude,
Mehrdad Zahra,
Noll Astrid,
Grabner ErichWalter,
Schmidt Reinhard
Publication year - 2001
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/1522-2675(20010919)84:9<2493::aid-hlca2493>3.0.co;2-f
Subject(s) - chemistry , benzophenone , photochemistry , excited state , quenching (fluorescence) , intramolecular force , triplet state , singlet oxygen , ketone , molecule , singlet fission , singlet state , ground state , oxygen , reaction rate constant , electron transfer , stereochemistry , fluorescence , kinetics , atomic physics , organic chemistry , physics , quantum mechanics
We have studied the charge‐transfer‐induced deactivation of n π * excited triplet states of benzophenone derivatives by O 2 ( 3 Σ ), and the charge‐transfer‐induced deactivation of O 2 ( 1 Δ g ) by ground‐state benzophenone derivatives in CH 2 Cl 2 and CCl 4 . The rate constants for both processes are described by Marcus electron‐transfer theory, and are compared with the respective data for a series of biphenyl and naphthalene derivatives, the triplet states of which have ππ * configuration. The results demonstrate that deactivation of the locally excited n π * triplets occurs by local charge‐transfer and non‐charge‐transfer interactions of the oxygen molecule with the ketone carbonyl group. Relatively large intramolecular reorganization energies show that this quenching process involves large geometry changes in the benzophenone molecule, which are related to favorable Franck‐Condon factors for the deactivation of ketone‐oxygen complexes to the ground‐state molecules. This leads to large rate constants in the triplet channel, which are responsible for the low efficiencies of O 2 ( 1 Δ g ) formation observed with n π * excited ketones. Compared with the deactivation of ππ * triplets, the non‐charge‐transfer process is largely enhanced, and charge‐transfer interactions are less important. The deactivation of singlet oxygen by ground‐state benzophenone derivatives proceeds via interactions of O 2 ( 1 Δ g ) with the Ph rings.