Quenching constant, high concentration effects

Whereas a straight Stem-Volmer plot could not be obtained in quenching studies with octafluomaphthalene, the orders of magnitude of the rate constants of triplet decay ka) and of reaction with olefin ( r) could still be estimated Ad = 6 X 10 s i and ki =2 X 10 1 mole is i >). In view of this rapid decay, a high concentration of olefin is evidently necessary for effective addition. 

One possible explanation for the lack of correspondence between emitting and reacting states is reaction of the singlet. In the case of benzophenone, there is little question that the reaction involves only the triplet state, since triplet quenchers can effectively inhibit the reaction. This need not be the case with all carbonyl compounds. For example, it has been shown that both the n,ir singlet and triplet states can be involved in the Norrish type II cleavage of alkyl ketones (25-27). At high concentrations, piperylene quenches only that part of the 2-hexanone cleavage which arises from the triplet. The rate constants for... 

The NaCl effect upon the proton-transfer reactions in the excited state of 2-naphthol has been studied by Harris and Selinger [41]. They have reported that the enhancement of the fluorescence of 2-naphthol is due either to a disruption of the water structure by the high concentration of Na and Cl ions or to an increase in the activity coefficient of the excited 2-naphthol. In previous works [53,106,107], it is shown that NaCl is a very weak quencher there is a weak quenching ability for CT, but no ability for Na. The NaCl effect on the proton dissociation reactions in water at 300 K has been studied by means of nanosecond and picosecond spectroscopy with fluorimetry [108]. The proton dissociation rate constant k decreases with an increase of [NaCl] according to the equation... 

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