Triplet energies, reduction potentials, and ionization potentials in carbonyl-donor partial charge-transfer interactions. I

Guttenplan, Joseph B.; Cohen, Saul G.

doi:10.1021/ja00766a079

Cited by 145 publications

(65 citation statements)

References 6 publications

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“…For the same chromophore, with a system of donors, AGcT and the logarithm of the rate constant of fluorescence quenching, k,, are linearly proportional to the ionization potential of the quencher (18). The relation for 2a and 26 is shown in hexane in Fig.…”

Section: Discussionmentioning

confidence: 99%

Thione photochemistry. Dual pathways in aralkyl thione cyclizations

Basu¹,

Couture²,

Ho³

et al. 1981

Can. J. Chem.

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It is shown that aralkyl thiones, which possess an oxygen atom at the δ position in the side chain, can therefore not undergo the preferred δ insertion, and insert at the γ and ε positions. Although ε insertion occurs only from the 1(π,π*) state, γ abstraction (followed by cyclization or cleavage) occurs from both 1(π,π*) and 3(n,π*) states. The quantum yields of photocyclization of 2c, 2d, and 2g change little with solvent polarity, which suggests that a thione–ether charge transfer interaction contributes little to the cyclization. Fluorescence and product quenching studies are reported which support this.

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Section: Discussionmentioning

confidence: 99%

Thione photochemistry. Dual pathways in aralkyl thione cyclizations

Basu¹,

Couture²,

Ho³

et al. 1981

Can. J. Chem.

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“…In contrast with highly fluorescent hydrocarbons, the excited singlet state of carbonyl compounds is so short-lived that most of the quenching reactions studied involve the triplet state. Guttenplan and Cohen (1972) found linear correlations between log k, for quenching of benzophenone triplet and the I P S of a number of aliphatic and aromatic donors. The aliphatic quenchers were correlated by one regression line, the aromatic by another with distinctly greater slope.…”

Section: Molecules Primarily Of Photochemical Interestmentioning

confidence: 94%

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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“…1). 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.…”

Section: Introductionmentioning

confidence: 99%

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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Triplet energies, reduction potentials, and ionization potentials in carbonyl-donor partial charge-transfer interactions. I

Cited by 145 publications

References 6 publications

Thione photochemistry. Dual pathways in aralkyl thione cyclizations

Thione photochemistry. Dual pathways in aralkyl thione cyclizations

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

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

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