Triplet benzophenone decay rate

The dependence of kp on the type of a-hydrogen is not known, nor can variations in ke be predicted easily. Mataga has studied amine quenching of triplet benzophenone by flash spectroscopy. N,N-dialkylanilines are the only amines which actually yield radical ions, and then only in polar solvents 157). He suggests two competing decay modes of the exciplex. Monoalkylanilines and tertiary aliphatic amines in any solvent and dialkylanilines in nonpolar solvents yield only radicals, presumably from the exciplex. Even though the oxidation potentials of tertiary aliphatic amines are so low that they quench triplet ketones at rates... 

CF,)jC,H4, 0-, m-, and p-FC,H4Me, o- and m-FC,HiCF PhF, - CeFe, and C,F6H has been studied, and trends in the radiative and non-radiative decay rates of the excited molecules are discussed. - c/s-But-2-ene is effective in increasing the fluorescent and triplet yields of pentafluorobenzene. The decay rate of triplet benzophenone, produced by laser flash photolysis, is ca. ten times faster in hexafluorobenzene than in benzene, and reversible addition of the triplet species to the aromatic ring may play an important role. The phosphorescence spectrum of decafluoro-benzophenone has been studied, and the triplet state of this ketone (see also p. 380) in inert solvents e.g. perfluoromethylcyclohexane) has a lifetime of 20 ps. U.v. irradiation of decafluorobenzophenone in isopropyl alcohol... 

The intermediate diphenylhydroxymethyl radical has been detected after generation by flash photolysis. Photolysis of benzophenone in benzene solution containing potential hydrogen donors results in the formation of two intermediates that are detectable, and their rates of decay have been measured. One intermediate is the PhjCOH radical. It disappears by combination with another radical in a second-order process. A much shorter-lived species disappears with first-order kinetics in the presence of excess amounts of various hydrogen donors. The pseudo-first-order rate constants vary with the structure of the donor with 2,2-diphenylethanol, for example, k = 2 x 10 s . The rate is much less with poorer hydrogen-atom donors. The rapidly reacting intermediate is the triplet excited state of benzophenone. 

The electron transfer step is typically fast and efficient. Griller et a/.292 measured absolute rate constants for decay of benzophenone triplet in the presence of aliphatic tertiary amines in benzene as solvent. Values lie in die range 3-4x109 M 1 s 1 and quantum yields are close to unity. 

That charge-transfer effects are not involved follows from the fact that the rate of triplet decay in perfluorobenzene is larger than that in benzene. If the benzophenone triplet were to act as acceptor and the benzene derivative as donor in a charge-transfer complex, the substitution of perfluorobenzene for benzene should render this type of process much less probable due to the strongly electron-withdrawing character of the fluorine atoms. 

The decay of the benzophenone triplet follows pseudo-first-order kinetics, and the experimental rate constant is related to the parameters of interest by Eq. 4,... 

The rate of benzophenone triplet decay is a combination of the unimolecular decay and the bimolecular reaction with the alcohol and can be described by ... 

Direct evidence for the formation of radical ion intermediates in the benzophenone-amine system was also obtained by Peters et al. [153-156]. Picosecond laser-flash photolysis studies have indicated the formation of ketyl radical anions concomitant with the decay of the benzophenone triplet. For 1.0 M dime-thylaniline and diethylaniline the rate of electron transfer to the benzophenone triplet was 3.6 x 10 and 4.2 x 10 m s , respectively. On the basis of their studies Peters et al. proposed a mechanism in which a solvent-separated ion pair... 

Koch and A.H. Jones, A photochemical exchange reaction of Michler s ketone, J. Am. Chem. Soc. 92, 7503 (1970) D.I. Schuster and M.D. Goldstein, Photochemistry of ketones in sol ution. XXXVII. Plash photolysis of Michler s ketone in solution. Rate constants for decay and triplet excimer formation, J. Am. Chem. Soc. 95, 986 (1973) V.D. McGinnis and D.M. Dusek, Photopolymerization of methyl methacrylate with the use of 4,4 BIS (diethylamion) benzophenone as the photoinitiator, ACS Polym. Prepr. 15(1), 480 (1974). 

Total Decay Constants, Relative Radiative Rates, Relative Populations, and Relative Populating Rates of the Lowest Triplet States OF Benzophenone and 4,4 -Dibromobenzophenone IN 4,4 -Dibromodiphenylether ... 

Annealing above T and slow cooling were found to affect the benzophenone phosphorescence decay in PMMA. The occurrence of quenching was ascertained by the rate constant for benzophenone triplet quenched by methyl acetate in an aceto-... 

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