Triplet benzophenone does not react efficientlywith aniline, o-toluidine, and diphenylamine to give isolable products. However, flash-photolysis studies showed that the ketone quite efficiently abstracts hydrogen from the amines.From a consideration of the kinetics of decay of the a-hydroxydiphenylmethyl radical, pathways were suggested whereby the radicals may react so as to produce the starting compounds. These results lead to a questioning of the assumption that primary and secondary aromatic amines act purely as physical quenchers for triplet ketones and the conclusion is reached that deactivation may be a result of either or both electron transfer and hydrogen-atom transfer. 9.1 O-Dihvdroacridine reacts with excited benzophenone, benzylideneacetophenone, and benzylideneacetone to give isolable reduction products.AN intriguing aspect of the photoreactions of aromatic carbonyl cornpodnds with aromatic tertiary amines l a p is that they take place by an electron-transfer mechanism. The nature of the intermediates produced by the electron transfer process, i.e., an exciplex or radical ions (see Scheme l), depends upon the polarity of the solvent. Kinetic measurements have shown that deactivation of the triplet ketone by the electron-transfer process is very efficient lb92 and flash-photolysis experiments have verified that radical-ion formation takes place in polar solvents.la9Backstrom and Sandros have reported3 upon the quenching of biacetyl phosphorescence by primary andsecondary aromatic amines and have shown that the rate constants for quenching approach the diff usion-controlled limit. In contrast, triphenylamine was found to be a less efficient quencher. Turro and Engel confirmed these results 4 and interpreted the quenching as occurring by electron transfer from the amine to the triplet ketone. If this mechanism is correct the efficiency of quenching should be related to the ionisation potential of the amine and consequently triphenylamine should be as good a quencher as aniline. In a related study, Cohen and Davis have reported that aniline and diphenylamine quench excited fluorenone much more readily than tri-~henylamine.~" However these workers did find that the quenching ability of a series of anilines was related to their ionisat ion PO t entialssb 1 (a) R.
Flash-photolysis experiments have shown that electronically excited fluorenone reacts with NN-dimethylaniline in polar solvents, to give the radical cation of the amine and the radical anion of the ketone. In benzene solution, the only radicals detected were the 9-hydroxyfluorenyl radical and the fluorenone radical anion. By the same technique, excited fluorenone was shown to react with triethylamine in both polar and non-polar solvents to give the fluorenone radical anion and the 9-hydroxyfluorenyl radical. The former radical is probably produced by dissociation of the latter radical. The photoreactions of fluorenone with amines are interpreted in terms of exciplex and radical ion intermediates.IT has been shown that fluorenone has a low-lying triplet state (probably m*) which is relatively unreactive, e.g.,
Abstract— The effects of flavone sulfonic acid 9 andquercetin–5′‐sulfonic acid 10 on the luminescence spectra of eight flavylium salts have been determined. The non‐hydroxylated flavone 9 was found to enhance the luminescence of those flavylium salts, while the polyhydroxyflavonol 10 was shown to exert the opposite effect. These findings are rationalized in conjunction with prior observations on the enhancement and inhibition of the photodecomposition of anthocyanins exerted by 9 and 10, respectively.
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