New intermediates in the reaction of benzophenone photoreduction by hydrogen donors

Tarasyuk, A. Yu.; Granchak, V. M.; Dilung, I. I.

doi:10.1016/1010-6030(94)03901-6

Cited by 14 publications

(7 citation statements)

References 25 publications

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“…The charge-transfer interaction involves the nitrogen lone pair of the amine as the donor and the azo chromophore as the acceptor, which is deficient in electron density by virtue of n,π* excitation. Such a partial charge transfer weakens the α C−H bond and facilitates abstraction of the hydrogen atom ( ) ) to the ground state (after intersystem crossing) accounts for the observed low efficiencies of the photoreduction (Table ).…”

Section: Discussionmentioning

confidence: 99%

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Charge-Transfer-Induced Photoreduction of Azoalkanes by Amines

et al. 1997

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The unique DBH-type azoalkanes 1, which exhibit high intersystem crossing quantum yields, have made possible the exploration of the bimolecular photoreduction of the n,π* triplet-excited azo chromophore. In the laser-flash photolysis, amines were found to quench the triplet azoalkane 1a with high rate constants (k q ca. 108 M-1 s-1). Steady-state photolysis of the azoalkanes 1a and 1b (φISC ca. 0.5) in the presence of primary, secondary, and tertiary aliphatic amines gave high chemical yields of the corresponding hydrazines 4a and 4b in competition with the unimolecular products, namely the housanes 2 and the aziranes 3. In contrast, the azoalkane 1c undergoes appreciable photoreduction only in neat amines, while the azoalkane 1d (φISC ca. 0.10) is not reduced even under such conditions. Except for N,N-dimethylbenzylamine, the amine oxidation products of the azoalkane photoreduction are analogous to those obtained from the reactions of amines with triplet benzophenone. In marked contrast, the absolute quantum yields of photoreduction for azoalkanes 1 are substantially lower (0.01−0.06) than for benzophenone (0.3−1.0). Efficient deactivation of the triplet-excited states by charge-transfer ( ), which competes with hydrogen atom abstraction ( ), is postulated to account for the low quantum yields. The efficiencies of photoreduction follow the trend primary ≈ tertiary ≫ secondary amines observed with benzophenone, for which secondary amines also display the poorest efficiency. Electron transfer to triplet-excited azoalkanes, analogous to benzophenone, is observed for amines with low oxidation potentials. Thus, when triphenylamine (E ox = 0.85 V versus SCE) is used, the formation of its radical cation can be readily detected by laser-flash photolysis.

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Section: Discussionmentioning

confidence: 99%

“…Such a partial charge transfer weakens the R C-H bond and facilitates abstraction of the hydrogen atom (k H CT ). 23 The unproductive radiationless decay of the charge-transfer complex (k q CT ) to the ground state (after intersystem crossing) accounts for the observed low efficiencies of the photoreduction (Table 2).…”

Section: Discussionmentioning

confidence: 99%

Charge-Transfer-Induced Photoreduction of Azoalkanes by Amines

et al. 1997

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“…The hydrogen abstraction reaction of an excited aromatic ketone in the presence of a hydrogen donor such as an amine, alcohol, ether or thiol is generally considered to be one of the best‐understood organic photochemical reactions. For example, photolysis of benzophenone in the presence of Bzh forms a pair of stable Bzh (ketyl) radicals, as a result of hydrogen atom abstraction (Scheme ) . This system has been used as a probe for the reaction since the resulting ketyl radical exhibits a strong absorption maximum at 535 nm .…”

Section: Resultsmentioning

confidence: 99%

Photoinduced reverse atom transfer radical polymerization of methyl methacrylate using camphorquinone/benzhydrol system

Taşkın

Yılmaz

Taşdelen

et al. 2013

Polymer International

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A versatile initiating system composed of camphorquinone/benzhydrol and Cu II Br 2 /N,N,N ,N ,N -pentamethyldiethyl enetriamine for photoinduced reverse atom transfer radical polymerization has been developed. The control experiments, where each component is eliminated in the reaction, serve as a direct verification of the mechanism. There is poor or no control over the polymerization of methyl methacrylate in the absence of either camphorquinone or benzhydrol. The experimental molecular weights are considerably higher than theoretical values and the obtained polymers show slightly broad molecular weight distributions ranging from 1.13 to 1.51 in the process. Although at relatively lower polymerization rates, the addition of an alkyl halide to the system leads to a better control of the polymerization as reflected by the improved molecular weight distribution and chain-end functionality.

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“…Thus in hydrogen-donating solvents, a hydrogen abstraction from the solvent molecules may proceed, resulting in formation of two intermediates: solute and solvent molecule radicals. If these two fragments can diffuse apart or reorient with respect to each other, a variety of stable photoproducts can be formed, − and photoreduction efficiency may particularly depend on the amount of the n,π* character in the triplet state, the strength of the C−H bond in the hydrogen donor, and the distance and orientation between carbonyl and donor molecule.…”

Section: Introductionmentioning

confidence: 99%

Continuous Irradiation Induced Luminescence from Benzophenone, 4,4‘-Dichlorobenzophenone, and 4-(Dimethylamino)benzaldehyde in Solid Environments and Its Pressure Dependence

Dreger

Drickamer

1997

J. Phys. Chem. A

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We report a strong emission change induced by continuous light irradiation in two ketones, benzophenone and 4,4‘-dichlorobenzophenone, and an aldehyde, 4-(dimethylamino)benzaldehyde, in their crystalline state as well as dissolved in solid polymers. With prolonged laser irradiation, a time evolution of the emission intensity shows complex features, but two clear competing trends can be distinguished: an increase and/or decrease of the emission intensity. It is shown that these trends may be a result of creation of either an emissive or a nonemissive species. The relative importance of these two pathways is significantly dependent on the type of medium and external pressure. The most characteristic feature of these dependencies is the fact that in crystalline environments, in contrast to polymers, the emission intensity at all pressures only decreases. A kinetic model is developed that assumes the lowest triplet state as the origin of the high photoreactivity of these molecules, causing their emission intensity change. This model embraces the observations either in crystalline or polymeric environments and is solved for two limiting cases: a predominance of the hydrogen abstraction reaction from the polymer or a predominance of the ionization due to biphotonic excitation of the triplet state. These processes are assumed responsible, respectively, for the creation of emissive and nonemissive photoproducts. By comparison of the model with experimental results some of the parameters involved in these processes are extracted and their pressure dependence can be predicted.

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New intermediates in the reaction of benzophenone photoreduction by hydrogen donors

Cited by 14 publications

References 25 publications

Charge-Transfer-Induced Photoreduction of Azoalkanes by Amines

Charge-Transfer-Induced Photoreduction of Azoalkanes by Amines

Photoinduced reverse atom transfer radical polymerization of methyl methacrylate using camphorquinone/benzhydrol system

Continuous Irradiation Induced Luminescence from Benzophenone, 4,4‘-Dichlorobenzophenone, and 4-(Dimethylamino)benzaldehyde in Solid Environments and Its Pressure Dependence

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