Nanosecond flash studies of reduction of benzophenone by aliphatic amines. Quantum yields and kinetic isotope effects

Inbar, Shai; Linschitz, Henry; Cohen, Saul G.

doi:10.1021/ja00395a009

Cited by 183 publications

(119 citation statements)

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“…The spectrum recorded at the end of the flash possesses strong absorptions at about 510 and 320 nm corresponding to BP triplets. 12 The ground-state absorption of PS + (λ max ) 518 nm) bleaches simultaneously with the decay of the BP triplet absorption at 320 nm. The bleaching process is paralleled by a buildup of a new absorption at 800 nm corresponding to 3 (PS + ) * .…”

Section: Reaction Of Ketonementioning

confidence: 99%

Photoinduced Energy and Electron Transfer between Ketone Triplets and Organic Dyes

et al. 1997

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Cationic organic dyes (phenosafranine, safranine T (ST + ), thiopyronine, and methylene blue) are efficient quenchers of the triplet states of aromatic ketones. The triplets of benzophenone (BP), xanthone, thioxanthone, benzil, and N-methylacridone are quenched by the dyes via energy transfer, generating triplet excited dyes (typically k q ) 5.5 × 10 9 M -1 s -1 for 3 BP * + ST + in acetonitrile solution). Regarding Michler's ketone, p-(dimethylamino)benzophenone, and 3,6-bis(dimethylamino)thioxanthone, the mechanism of triplet quenching is solvent-dependent. Electron transfer occurs in polar solvents like acetonitrile, and energy transfer is the dominant reaction pathway in less polar solvents, such as dichloromethane. Delayed fluorescence of the dye caused by heterotriplet-triplet annihilation involving ketone and dye was detected upon studying the reaction of the dyes with triplet excited ketones (BP, xanthone, thioxanthone, and benzil). By applying two successive laser pulses (λ ex ) 532 and 308 nm, respectively), the rate constant of the reaction 3 BP * + 3 (ST + ) * was determined: k ht ) 1.1 × 10 10 M -1 s -1 .

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Section: Reaction Of Ketonementioning

confidence: 99%

Photoinduced Energy and Electron Transfer between Ketone Triplets and Organic Dyes

et al. 1997

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“…While a 'direct' hydrogen abstraction competes in some cases, 1 the dominant photochemical process is assumed to involve electron transfer in the case of ketones. [2][3][4] The primary radical ion pair may undergo proton transfer or back electron transfer which results in an overall hydrogen transfer or deactivation, respectively. In support of this mechanism, quenching rate constants generally increase with decreasing ionization potential of the quencher and increasing solvent polarity unless specific solvation, 3,5,6 steric 4 or stereoelectronic effects 7,8 operate.…”

Section: Introductionmentioning

confidence: 99%

“…intermediates with partial charge-transfer character, has been suggested in the quenching of n,p*-excited ketones and azoalkanes by amines. 3,7,[9][10][11][12] Since direct spectroscopic detection through exciplex emission has not been achieved, reduced quantum yields 11,13 , small or 'inverted' solvent effects, 9,12,14 steric hindrance effects 15 , a low sensitivity of the quenching rate constants on the donor propensity of the quencher, 9 and related observations for olefins and aromatic quenchers [16][17][18][19][20][21] have been taken as indirect experimental indications for exciplexes.…”

Section: Introductionmentioning

confidence: 99%

Quenching of n,?*-excited azoalkanes by amines: structural and electronic effects on charge transfer

Pischel

Nau

2000

J. Phys. Org. Chem.

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“…OMKs were found to be slightly higher effective than the corresponding small molecular analog (2FBP2P and 2FBP2P). Although aliphatic NH transfers H efficiently to triplet carbonyl chromophore, the ketyl and aliphatic alkylaminyl (Ncentered) radicals largely react to regenerate starting materials, as had been validated by low quantum yield of reductions of BP by primary and secondary amines [20]. It is one of the possible reason that aliphatic tertiary amine as a co-initiator appears to be more popular than secondary amine in the formulation of UV-curing.…”

Section: Photochemistry and Photopolymerizationmentioning

confidence: 99%

A study on hybrid oligomeric type II photoinitiator

Kan

Yang

et al. 2010

E-Polymers

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Preparing tailor-made hybrid photoinitiator (PI) for specific applications continues to gain momentum. The hybrid PIs comprising both H-abstraction chromophore and coinitiator moiety are the candidate materials with energy-saving and environment-protection in the photo-curing field. So two oligomeric photoinitiators (OMKs) containing benzophenone (BP) and aliphatic tert-amines chromophore in the main-chain (OMK-2) or side-chain (OMK-1) were synthesized and characterized respectively. Photophysical investigation showed that the absorption maxima of OMKs were around 340 nm, red shifted about 5-10 nm compared to BP. Their initiation efficiencies were found to be higher than that of BP and 4,4"-bis(dimethylamino)benzophenone(MK) respectively. The reaction proceeds via a simple electron-transfer/proton-transfer mechanism. Dynamic NMR data reveal that H-abstraction reacts predominantly via alpha H of aliphatic tertamines, as might be expected on the basis of the lower ionization potential and bond dissociation energy of aliphatic amines compared to aromatic amines. The reaction mechanism of H-abstraction was confirmed by using radical scavenger 2,2,6,6-tetramethylpiperidin-1-oxy(TEMPO), which acts as a probe under photolysis reaction conditions. The volatility and migration were tested under simulated conditions, the result show that OMKs exhibited very low volatility and significantly reduced migration compared to the low molecular analogs. Results showed that the OMKs are the promising candidate as higher efficient PIs with low volatile organic compounds (VOCs) emission and reduced migration. They are suitable for environmental-friendly formulations.

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Nanosecond flash studies of reduction of benzophenone by aliphatic amines. Quantum yields and kinetic isotope effects

Cited by 183 publications

References 0 publications

Photoinduced Energy and Electron Transfer between Ketone Triplets and Organic Dyes

Photoinduced Energy and Electron Transfer between Ketone Triplets and Organic Dyes

Quenching of n,?*-excited azoalkanes by amines: structural and electronic effects on charge transfer

A study on hybrid oligomeric type II photoinitiator

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