Effect of water on the phosphorescence spectra of aromatic carbonyl compounds. Part 2.—Dual phosphorescence of benzophenone at 77 K in ethanol–water

Nakayama, Toshihiro; Sakurai, Kazumitsu; Hamanoue, Kumao; Otani, Akira

doi:10.1039/ft9918701509

Cited by 19 publications

(12 citation statements)

References 33 publications

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“…The acid−base properties − and hydrogen-bonding characteristics − of aromatic ketone triplets have been studied in detail. Protonation of benzophenone triplets by sulfuric acid in aqueous alcohol 31 or acetonitrile 32,33 solution proceeds rapidly ( k H+ ∼ 5 × 10 9 M -1 s -1 ) and reversibly, and leads to quenching of the triplet via rapid decay of the protonated species by intersystem crossing ( k ∼ 8 × 10 7 s -1 ) .…”

Section: Discussionmentioning

confidence: 99%

Photoinduced Hydrogen Abstraction from Phenols by Aromatic Ketones. A New Mechanism for Hydrogen Abstraction by Carbonyl n,π* and π,π* Triplets

1996

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Nanosecond laser flash photolysis studies have been carried out of the kinetics of inter- and intramolecular phenolic hydrogen abstraction by alkoxyacetophenone, 5-alkoxyindanone, and 4-alkoxybenzophenone triplets in acetonitrile and benzene solution. Information on the geometric requirements for abstraction by carbonyl n,π* and π,π* triplets is derived from the results for a series of ketones which contain a para-phenolic moiety attached via a para-oxyethyl linkage. For all of these compounds, the deuterium kinetic isotope effect on the triplet lifetime in acetonitrile solution indicates that triplet decay is determined by the rate of intramolecular abstraction of the remote phenolic hydrogen, which yields the corresponding phenoxyl−hemipinacol biradical. The biradicals have also been detected, and are about an order of magnitude longer-lived than the triplet in each case. For three of the compounds, the rates of the intramolecular process follow the same trend as that observed in the rates of bimolecular quenching of the parent methoxy-substituted ketones by p-cresol. Deviation from this trend is observed for the alkoxyindanone derivative, where an in-plane approach of the phenolic hydrogen to the carbonyl n-orbital is not possible. The trends in the rate constants for bimolecular quenching of a series of substituted benzophenones by p-cresol indicate that for n,π* triplet abstractions, the quenching mechanism is different for electron donor-substituted and electron acceptor-substituted ketones. For π,π* triplets and donor-substituted (n,π* triplet) benzophenones, abstraction is proposed to occur by a mechanism involving the intermediacy of a hydrogen-bonded exciplex, which yields the corresponding radicals by sequential electron- and proton-transfer. The rate constant for quenching by this mechanism thus depends mainly on the basicity of the ketone triplet state and the oxidation potential of the phenol.

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Section: Discussionmentioning

confidence: 99%

Photoinduced Hydrogen Abstraction from Phenols by Aromatic Ketones. A New Mechanism for Hydrogen Abstraction by Carbonyl n,π* and π,π* Triplets

1996

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“…It is well-known that solvent polarity affects the electronic structure of the excited triplet states of carbonyl compounds. The T 1 state characters of the carbonyl molecules with small energy separation between the 3 nπ*− 3 ππ* states are significantly sensitive to the matrix polarity. − On the other hand, for benzophenone, the complex formation with water is essential to change the T 1 state character from 3 nπ* to mixed 3 nπ*− 3 ππ*. , The energy levels of 3 nπ* states are destabilized more than those of 3 ππ* by the solvation with polar molecules or hydrogen bond formation with protic solvents.…”

Section: Introductionmentioning

confidence: 99%

Substituent and Matrix Effects on the Excited Triplet States of 1,4-Naphthoquinones

Shimokage¹,

Ikoma²,

Akiyama³

et al. 1997

J. Phys. Chem. A

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Phosphorescence and TREPR spectra have been measured for 2-methyl-1,4-naphthoquinone (MNQ), 2,3-dimethyl-1,4-naphthoquinone (DMNQ), and 2-methoxynaphthoquinone (MeONQ) in several matrices at low temperatures. The |D| value of ZFS parameter decreases with increasing the electron-donating character of the substituent group. For MNQ, the T1 state is clearly assigned to be 3nπ* in character. The broad phosphorescence spectra and minor effects of the matrix polarity on the ZFS parameters lead to the conclusion that the character of the T1 states are mainly 3ππ* in DMNQ and MeONQ. The T1 states of the present naphthoquinone derivatives have more or less mixed character of the 3nπ* and 3ππ* states.

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“…They can be assigned to the n−π* orbital transition of BP maximizing at ∼350 nm and also the π−π* orbital transition, which occurs at shorter wavelength and peaks at ∼250 nm. Upon excitation of BP in the (n, π*) band, the phosphorescence spectrum due to a radiative transition from the excited triplet state to the ground state is observed at around 400−500 nm. − Figure shows the phosphorescence spectra of BP in the CCl 4 solution and BP adsorbed on porous Vycor glass at a low surface coverage (2 × 10 -6 mol/g) at 77 K. In the nonpolar solution of CCl 4 (10 -2 M), the phosphorescence spectrum of BP at 77 K exhibits well-structured vibrational fine structures due to the CO groups of BP. (Figure (5)).…”

Section: Resultsmentioning

confidence: 99%

Characteristics of the Phosphorescence Spectra of Benzophenone Adsorbed on Ti−Al Binary Oxides

2001

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The excited states of benzophenone adsorbed on well-characterized Ti−Al binary oxides were investigated by means of conventional molecular spectroscopic techniques such as UV and IR absorption as well as photoluminescence spectra measurements. It was found that the photochemical and photophysical properties of benzophenone adsorbed on the oxide surfaces strongly depend on their surface properties, which are systematically changed by changing the composition of the oxides. Specifically, the phosphorescence spectra of benzophenone adsorbed on the oxides have been found to be composed of the hydrogen-bonded benzophenone species and the protonated benzophenone species.

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Effect of water on the phosphorescence spectra of aromatic carbonyl compounds. Part 2.—Dual phosphorescence of benzophenone at 77 K in ethanol–water

Cited by 19 publications

References 33 publications

Photoinduced Hydrogen Abstraction from Phenols by Aromatic Ketones. A New Mechanism for Hydrogen Abstraction by Carbonyl n,π* and π,π* Triplets

Photoinduced Hydrogen Abstraction from Phenols by Aromatic Ketones. A New Mechanism for Hydrogen Abstraction by Carbonyl n,π* and π,π* Triplets

Substituent and Matrix Effects on the Excited Triplet States of 1,4-Naphthoquinones

Characteristics of the Phosphorescence Spectra of Benzophenone Adsorbed on Ti−Al Binary Oxides

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