Competitive Energy and Electron-Transfer Reactions of the Triplet State of 1-Nitronaphthalene:  A Laser Flash Photolysis and Time-Resolved Resonance Raman Study

Fournier, Thierry; Tavender, Susan M.; Parker, Anthony W.; Scholes, Gregory D.; Phillips, David

doi:10.1021/jp970470o

Cited by 36 publications

(39 citation statements)

References 56 publications

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“…The nature of the 1NN triplet state has been the subject of discussion: some authors suggested a π -π* state, others a n -π* state, while some even suggest that the lowest energy state is correlated with the increase in solvent polarity, switching from n -π* to π -π*. Fournier and co-workers 27 demonstrated that in polar solvents (e.g. water) the dipolar π -π* should be more stable than n -π*.…”

Section: Resultsmentioning

confidence: 99%

“…Although the halogen radicals can initiate a set of catalytic cycles capable of destroying ozone 26 or of oxidizing organic compounds (R2 and R3), to our knowledge only a limited number of studies have investigated their formation via photosensitized reactions of organic compounds in the atmospheric aqueous phase. The interaction between the excited state of 1NN ( 3 1NN) and halides has previously been reported in ethanol-water solution 27 . The H-atom abstraction between 3 1NN and ethanol, reported by the cited authors as the main reaction, suggests that the interaction between 1NN and halides could be affected by a solvent-triplet state interaction.…”

Section: Introductionmentioning

confidence: 83%

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Photochemistry of 1-Nitronaphthalene: A Potential Source of Singlet Oxygen and Radical Species in Atmospheric Waters

et al. 2010

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Abstract1-Nitronaphthalene (1NN) was used as a model of nitro-PAHs to investigate photosensitized reactions in aqueous solution in the presence of oxygen and halides. Laser Flash Photolysis (LFP) was employed to investigate electron transfer between halide anions and the triplet state of 1NN, leading to the formation of dihalogen radical anions (X 2 •-) in solution. The experiments were performed in the absence or presence of oxygen, showing a bimolecular quenching rate constant for the triplet state of 1NN ( 3 1NN) by oxygen of (1.95 ± 0.05) × 10 9 M -1 s -1 . The decay of 3 1NN was observed to strongly depend on the pH of the medium. At pH > 2, 3 1NN decayed with a pseudo-first order rate constant close to 6.0 × 10 5 s -1 . The rate constant was markedly enhanced at lower pHs, reaching 2.0 × 10 6 s -1 at pH ~ 0.1, which suggests formation of the protonated triplet state ( 3 1NNH + ) at low pHs. Furthermore, we showed that the photoreactions of 3 1NN in the presence of oxygen are potential sources of HO 2 • , 1 O 2 and possibly • OH in aqueous media. In Milli-Q water (pH ~ 6.5) and in the presence of halide anions the quenching rate constant of 3 1NN was evaluated to be (2.9 ± 0.4) × 10 4 M -1 s -1 for chloride, (7.5 ± 0.2) × 10 8 M -1 s -1 for bromide, and (1.1 ± 0.1) × 10 10 M -1 s -1 for iodide. Also in this case a pH-dependent reactivity was evidenced, and the quenching rate constant was (7.7 ± 1.2) × 10 5 M -1 s -1 with chloride at pH 1.1.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 83%

Photochemistry of 1-Nitronaphthalene: A Potential Source of Singlet Oxygen and Radical Species in Atmospheric Waters

et al. 2010

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“…ion pairs and exciplexes is still unknown. Time-resolved vibrational spectroscopy, which has been very scarcely used in this field [119][120][121][122], should give a new insight. Time-resolved multidimensional IR spectroscopy, which is just emerging [123,124], might prove to be a powerful tool to investigate the geometry of these bimolecular complexes.…”

Section: Discussionmentioning

confidence: 99%

Investigations of bimolecular photoinduced electron transfer reactions in polar solvents using ultrafast spectroscopy

Vauthey

2006

Journal of Photochemistry and Photobiology A: Chemistry

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Several controversial questions in the field of bimolecular photoinduced electron transfer reactions in polar solvents are first briefly reviewed. Results obtained in our group using ultrafast spectroscopy and giving a new insight into these problems will then be described. They concern the driving force dependence of the charge separation distance, the formation of the reaction product in an electronic excited state, the absence of normal region for weakly exergonic charge recombination processes and the excitation wavelength dependence of the CR dynamics of donor-acceptor complexes.

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“…[2][3][4][5] Because of this efficient ISC and thus large triplet yield, the photochemistry of most nitroaromatic compounds essentially takes place from the T 1 state. [6][7][8][9][10] More recently, the fluorescence decays of a series of polycyclic nitroaromatic hydrocarbons such as 1-nitronaphthalene, 9-nitroanthracene, and 1-nitropyrene in methanol have been shown to be ultrafast, with average time constants on the subpicosecond time scale. 11,12 These very small lifetimes have been ascribed to highly efficient ISC, and as a result, these compounds can be considered as the organic molecules with the fastest ISC.…”

Section: Introductionmentioning

confidence: 99%

Excited-State Dynamics of Nitroperylene in Solution: Solvent and Excitation Wavelength Dependence

2008

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The photophysics and excited-state dynamics of nitroperylene (NPe) in solvents of various polarities and viscosities, including a room-temperature ionic liquid, have been investigated by femtosecond-resolved transient absorption spectroscopy. The excited-state absorption spectrum was found to depend substantially on solvent polarity. In the most polar solvents, it is very similar to that of the NPe radical cation generated upon bimolecular quenching by an electron acceptor, denoting a substantial charge-transfer character of the S 1 state. Contrary to smaller nitroaromatic compounds, NPe in the S 1 state does not undergo ultrafast intersystem crossing (ISC) but decays mainly by internal conversion (IC). In nonprotic solvents, IC involves low-frequency modes with large amplitude motion associated with the nitro group and depends on both the solvent viscosity and polarity. It takes place on a 100 ps time scale in acetonitrile, while in cyclohexane, it is slow enough for ISC to become competitive. Moreover, both the fluorescence quantum yield and the excited-state dynamics were found to differ, depending on which side of the S 0 -S 1 absorption band excitation was performed. This dependence is explained by the inhomogeneous nature of the absorption spectrum arising from a distribution of twist angles of the nitro group relative to the aromatic plane. On the other hand, such excitation wavelength effects were not observed in protic solvents, where the excited-state lifetime was found to be substantially shorter than that in nonprotic solvents. This behavior is rationalized in terms of a H-bonding interaction, which limits the torsional disorder of NPe and favors ultrafast nonradiative deactivation of the excited state. Transient absorption measurements performed for comparative purpose with nitropyrene in acetonitrile confirm the occurrence of ultrafast ISC in smaller nitroaromatic compounds.

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Competitive Energy and Electron-Transfer Reactions of the Triplet State of 1-Nitronaphthalene: A Laser Flash Photolysis and Time-Resolved Resonance Raman Study

Cited by 36 publications

References 56 publications

Photochemistry of 1-Nitronaphthalene: A Potential Source of Singlet Oxygen and Radical Species in Atmospheric Waters

Photochemistry of 1-Nitronaphthalene: A Potential Source of Singlet Oxygen and Radical Species in Atmospheric Waters

Investigations of bimolecular photoinduced electron transfer reactions in polar solvents using ultrafast spectroscopy

Excited-State Dynamics of Nitroperylene in Solution: Solvent and Excitation Wavelength Dependence

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