Laser photolysis studies of duroquinone triplet state electron transfer reactions

Scheerer, R.; Gräetzel, Michael

doi:10.1021/ja00445a032

Cited by 104 publications

(55 citation statements)

References 5 publications

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“…The quenching could not be followed at 280 nm but the growth of the diphenylaminyl radical cation could be observed. The spectrum, with a maximum at 680nm in the visible region is in good agreement with literature values (14)(15)(16). The quenching plot with a representative trace showing diphenylaminyl radical cation growth kinetics is shown in Fig.…”

Section: B Quenching With Other Aminessupporting

confidence: 89%

A reinvestigation of the interaction between triplet states of cyclohexenones and amines

Weir¹,

Scaiano²,

Schuster³

1988

Can. J. Chem.

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. J. Chem. 66, 2595Chem. 66, (1988.Laser flash photolysis studies lead to the conclusion that the short-lived triplet states of cyclohexenones are readily quenched by amines. For example, in the case of 2-cyclohexen-1-one (I) its triplet state (TT = 40 ns in acetonitrile) is quenched by triethylamine with a rate constant of (9.0 2 0.8) x lo7 M-' s-I. Cyclohexenone triplets are also quenched efficiently by DABCO and by triphenylamine leading to the formation of the corresponding amine radical cations. The new evidence reported rules out the involvement of long-lived detectable exciplexes. Cohen and Peters and their co-workers have studied this process with benzophenone and related ketones, and have demonstrated convincingly that the quenching process involves electron transfer to give initially amine radical cations and ketone radical anions (2). Schuster and Brisimitzakis demonstrated that reactive 2,5-cyclohexadienone triplets are quenched by amines of appropriate ionization potential to give a set of products not observed in the absence of amines. In all cases, the amine interacts directly with ketone triplet (3).Reactions of photoexcited a,~-unsaturated carbonyl compounds with amines are known to give 1:l adducts, presumably via the enone triplet states (4). Dunn et al. have reported results of nanosecond flash studies on excitation of cvclohexanone I and analogues such as I1 (see Chart I) in the presence of 1,4-diazabicyclo [2.2.2]octane (DABCO) which demonstrate that long-lived DABCO radical cations (X,,, 450 nm) are formed from an intermediate which has the same lifetime (ca. 25 ns) as the transient species (X,,, 280 nm) generated on laser excitation of the enone in the absence of amines (5). This transient has been suggested by Bonneau (6) and by Schuster et al. (7) to be a highly twisted triplet excited state of these cyclohexenones. In the presence of even small amounts of DABCO, long-lived absorption is observed which interferes with analysis of the fast component of the decay curve at wavelengths in the range 270-300 nm; at the DABCO concentrations required for observation of the growth of the radical cation at 450 nm, the fast decay at 280 nm cannot be monitored (5,8).In contrast to the above findings, Pienta and McKimmey reported results of product analyses from excitation of I in the

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Section: B Quenching With Other Aminessupporting

confidence: 89%

A reinvestigation of the interaction between triplet states of cyclohexenones and amines

Weir¹,

Scaiano²,

Schuster³

1988

Can. J. Chem.

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“…In order to characterize the triplet excited state of MG, the technique of triplet-triplet energy transfer sensitization was used. The sensitizer chosen for this purpose was the DQ (E T ¼ 24,600 cm À1 [58]). The mechanism of the triplet-triplet sensitization process is shown in the Scheme 3.…”

Section: Resultsmentioning

confidence: 99%

An experimental and theoretical study on the photophysical properties of methylene green

et al. 2011

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“…Yang et al (1977) discuss the role of exciplexes in the quenching of acetone, norcamphor and other ketone fluorescence by dienes and other quenchers. Scheerer and Gratzel (1977) plotted rate constants for quenching of triplet state duroquinone against WT -EL + EA for a series of quenching donors in aqueous ethanol. From Eq.…”

Section: Molecules Primarily Of Photochemical Interestmentioning

confidence: 99%

The Energetics of Electron‐transfer Reactions of Chlorophyll and Other Compounds*

Seely

1978

Photochem & Photobiology

164

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Abstract-Quite often the primary photochemical reaction of an excited state molecule is transfer of an electron to or from another molecule in its ground state. Rates of such reactions are closely dependent on differences between ground and excited state redox potentials of the reagents. The solvent also plays an important role in stabilizing ion pairs formed by the electron transfer. This Review discusses experimental data relating rates to electrochemical energy parameters in the context of a scheme which portrays the energy and electron transactions in a unified manner. Three consequences of reaction of a singlet excited state are distinguished: (Sl) quenching without detectable products, (S2) exciplex fluorescence, (S3) transient radical ion production, and energetically necessary conditions are derived for each. Similarly, four kinds of reactions involving the triplet state are distinguished, which depend on the relation between the energy of the triplet state and that of the ion pair states: (TI) rapid quenching, (T2) slow quenching, (T3) accelerated intersystem crossing and (T4) generation by reaction between radical ions 'of like spin. The last may be followed by electrochemiluminescence. Classes of compounds for which data are available include chlorophylls, porphyrins and a few other molecules of biological interest, aromatic hydrocarbons and their derivatives, heterocyclic systems, carbonyl compounds, dyes, and complexes of Ru and U. A Table compiling median or selected values of ground and excited state electrochemical potentials of chlorophylls, some porphyrins, and a few other compounds is presented.

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Laser photolysis studies of duroquinone triplet state electron transfer reactions

Cited by 104 publications

References 5 publications

A reinvestigation of the interaction between triplet states of cyclohexenones and amines

A reinvestigation of the interaction between triplet states of cyclohexenones and amines

An experimental and theoretical study on the photophysical properties of methylene green

The Energetics of Electron‐transfer Reactions of Chlorophyll and Other Compounds*

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