Intramolecular quenching of carbonyl triplets by .beta.-phenyl rings

Autor:	T. Kilp, T. Wismontski-Knittel
Rok vydání:	1984
Předmět:	chemistry.chemical_classification Quenching (fluorescence) Ketone Chemistry General Engineering Hydrogen atom abstraction Photochemistry chemistry.chemical_compound Electron transfer Reaction rate constant Propiophenone Intramolecular force Physical and Theoretical Chemistry Triplet state
Zdroj:	The Journal of Physical Chemistry. 88:110-115
ISSN:	1541-5740 0022-3654
DOI:	10.1021/j150645a028
Popis:	The presence of a phenyl ring in a position ..beta.. to the carbonyl of a phenyl alkyl ketone results in greatly reduced ketone triplet lifetimes. For example, in deaerated benzene solutions, triplet lifetimes were 2700 and 0.89 ns for propiophenone (P) and ..beta..-phenylpropiophenone (PP) and 3500 and 50 ns for 4'-methoxypropiophenone (MeOP) and ..beta..-phenyl-4'-methoxypropiophenone, respectively. Triplet energy transfer from the ketones to 1-methylnapthalene (MeN) proceeded at nearly diffusion-controlled rates. The rate of electron transfer from the triplet carbonyls to methylviologen was also found to be very efficient, occurring with rate constants of 8.8 X 10/sup 9/ and 8.3 X 10/sup 9/ M/sup -1/ s/sup -1/ for MeOP and PMeOP, respectively. From the triplet decays and the shapes of the triplet-triplet absorbance spectra, a quenching mechanism involving intramolecuular hydrogen abstraction was ruled out. A process involving an exciplex intermediate, characterized by a degree of charge transfer (CT), was proposed as the likely mechanism for the intramolecular quenching of triplet lifetimes in PP and PMeOP. 6 figures, 2 tables
Databáze:	OpenAIRE
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