Role of the lower triplet state in photoreactions of aromatic amines

Malkin, Ya. N.; Ruziev, Sh.; Pirogov, N. O.; Кузьмин, В. А.

doi:10.1007/bf00953844

Cited by 7 publications

(5 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This indicates dissociation originating from the singlet state, although in the case of compound 1 we identified the triplet state (Figure ) as the dissociating state giving PhCH 2 • ; pressumably both are involved in the dissociation process. Here we should note the debate 19,23 regarding the responsible excited state(s) for the N−H photodissociation in PhNH 2 ; Malkin et al considered that photodissociation occurs mainly from the T 1 state, while Köhler and Getoff 23b and Saito, Tobita, and Shizuka 22b concluded that most of the formation of PhNH • takes place from the S 1 state.…”

Section: Resultsmentioning

confidence: 93%

See 1 more Smart Citation

Photodissociation ofN-Arylmethylanilines: A Laser Flash Photolysis, Fluorescence, and Product Analysis Study¹

et al. 1999

View full text Add to dashboard Cite

Increased phenylation in the molecular series PhCH(2)NHPh (1), Ph(2)CHNHPh (2), and Ph(3)CNHPh(3) has two important consequences on the photophysical/photochemical behavior: (i) decrease in the fluorescence quantum yields (cyclohexane), Phi(f) = 0.115, 0.063, 0.001 (lambda(exc) = 254 nm) and 0.164, 0.089, 0.019 (lambda(exc) = 290 nm), respectively, and (ii) increase in the quantum yield (MeCN) of the photodissociation products PhCH(2)(*), Ph(2)CH(*), and Ph(3)C(*), Phi(radical) = 0.16, 0.25, 0.65 (lambda(exc) = 248 nm) and (not measured), 0.18, 0.29 (lambda(exc) = 308 nm), respectively. As the C-N bond progressively weakens in the series 1, 2, 3 (bond dissociation enthalpy: 52, 48, 39 kcal/mol, respectively), the C-N fission channel becomes obviously more favorable and competes effectively with fluorescence. The involved intermediates PhCH(2)(*), Ph(2)CH(*), Ph(3)C(*), and PhNH(*) were identified using laser flash photolysis (248 and 308 nm). Product analysis (lamp irradiation) gives as main products aniline and (i) 1,1-diphenylethane and o- and p-benzylaniline for 1, (ii) 1,1,2,2-tetraphenylethane for 2, (iii) Ph(3)CH and 9-Ph-fluorene for 3; all these compounds are formed from the above radicals through coupling or H-abstraction reactions.

show abstract

Section: Resultsmentioning

confidence: 93%

“…Fluorescence quantum yields were measured by comparison with values reported for aniline: Φ f = 0.17 (λ exc = 290-nm) and Φ f = 0.11 (λ exc = 254-nm) in cyclohexane solutions (OD 290 nm = 0.25/cm, OD 254 nm = 0.60/cm).…”

Section: Methodsmentioning

confidence: 99%

Photodissociation ofN-Arylmethylanilines: A Laser Flash Photolysis, Fluorescence, and Product Analysis Study¹

et al. 1999

View full text Add to dashboard Cite

show abstract

“…However, photolysis directly populates the lower-energy excited states, which tend to dissociate into radical fragments that are the precursors of diphenylamine. Dissociation is especially efficient from the triplet excited state of aniline . Taking into account the high yield of intersystem crossing (Φ ISC = 0.68) for the process S 1 → T 1 in aniline, the 254 and 185 nm excitation used in this work should populate well the lowest-energy triplet excited state of aniline with some additional vibrational excitation, which would lead to efficient dissociation and eventually to the formation of diphenylamine in high yields.…”

Section: Resultsmentioning

confidence: 99%

“…The conclusion is that the triplet excited state is a precursor to at least part of the ammonia and diphenylamine. Work elucidating the role of the lower-energy excited states in photoreactions of aromatic amines has suggested that the photodissociation (RNH 2 → RNH• + H•) reaction takes place from both lowest-energy singlet and triplet excited states of aniline, but the process occurs more efficiently from the triplet excited state . This photodissociation reaction creates the aminyl radical, which is one of diphenylamine precursors.…”

Section: Resultsmentioning

confidence: 99%

Role of the Low-Energy Excited States in the Radiolysis of Aromatic Liquids

2011

View full text Add to dashboard Cite

The contribution of the low-energy excited states to the overall product formation in the radiolysis of simple aromatic liquids--benzene, pyridine, toluene, and aniline--has been examined by comparison of product yields obtained in UV-photolysis and in γ-radiolysis. In photolysis, these electronic excited states were selectively populated using UV-light excitation sources with various energies. Yields of molecular hydrogen and of "dimers" (biphenyl, bibenzyl, dipyridyl for benzene, toluene, pyridine, respectively, and of ammonia and diphenylamine for aniline) have been determined, since they are the most abundant radiolytic products. Negligibly small production of molecular hydrogen in the UV-photolysis of aromatic liquids with excitation to energies of 4.88, 5.41, 5.79, and 6.70 eV and the lack of a scavenger effect suggest that this product originates from short-lived high-energy singlet states. A significant reduction in "dimer" radiation-chemical yields in the presence of scavengers such as anthracene or naphthalene indicates that the triplet excited states are important precursors to these products. The results for toluene and aniline suggest that efficient dissociation from the lowest-energy excited triplet state leads to noticeable "dimer" production. For benzene and pyridine, the lowest-energy triplet excited states are not likely to fragment into radicals because of the relatively large energy gap between the excited state level and corresponding bond dissociation energy. The "dimer" formation in the radiolysis of benzene and pyridine is likely to involve short-lived high-energy triplet states.

show abstract

“…Fluorescence emission and excitation spectra were obtained on a Edinburgh FS900 spectrofluorimeter. Fluorescence quantum yields were measured by comparison with the reported values for aniline (Φ f = 0.17 and 0.11 in cyclohexane with excitation wavelengths λ ex = 290 and 254 nm, respectively, and Φ f = 0.15 in MeCN with excitation wavelength λ ex = 290 nm). Fluorescence lifetimes were measured using a time-correlated single-photon counter.…”

Section: Methodsmentioning

confidence: 99%

Mechanism of the Photodissociation of 4-Diphenyl(trimethylsilyl)methyl-N,N-dimethylaniline

et al. 2000

View full text Add to dashboard Cite

On irradiation in hexane (248- and 308-nm laser light) 4-diphenyl(trimethylsilyl)methyl-N,N-dimethylaniline, 2, undergoes photodissociation of the C-Si bond giving 4-N,N-dimethylamino-triphenylmethyl radical, 3(*) (lambda(max) at 343 and 403 nm), in very high quantum yield (Phi = 0.92). The intervention of the triplet state of 2 (lambda(max) at 515 nm) is clearly demonstrated through quenching experiments with 2,3-dimethylbuta-1,3-diene, styrene, and methyl methacrylate using nanosecond laser flash photolysis (LFP). The formation of 3(*) is further demonstrated using EPR spectroscopy. The detection of the S(1) state of 2 was achieved using 266-nm picosecond LFP, and its lifetime was found to be 1400 ps, in agreement with the fluorescence lifetime (tau(f) = 1500 ps, Phi(f) = 0.085). The S(1) state is converted almost exclusively to the T(1) state (Phi(T) = 0.92). In polar solvents such as MeCN, 2 undergoes (1) photoionization to its radical cation 2(*)(+), and (2) photodissociation of the C-Si bond, giving radical 3(*) as before in hexane. The formation of 2(*)(+) occurs through a two-photon process. Radical cation 2(*)(+) does not fragment further, as would be expected, to 3(*) via a nucleophile(MeCN)-assisted C-Si bond cleavage but regenerates the parent compound 2. Obviously, the bulkiness of the triphenylmethyl group prevents interaction of 2(*)(+) with the solvent (MeCN) and transfer to it of the electrofugal group Me(3)Si(+). The above results of the laser flash photolysis are supported by pulse radiolysis, fluorescence measurements, and product analysis.

show abstract

Role of the lower triplet state in photoreactions of aromatic amines

Cited by 7 publications

References 8 publications

Photodissociation ofN-Arylmethylanilines: A Laser Flash Photolysis, Fluorescence, and Product Analysis Study¹

Photodissociation ofN-Arylmethylanilines: A Laser Flash Photolysis, Fluorescence, and Product Analysis Study¹

Role of the Low-Energy Excited States in the Radiolysis of Aromatic Liquids

Mechanism of the Photodissociation of 4-Diphenyl(trimethylsilyl)methyl-N,N-dimethylaniline

Contact Info

Product

Resources

About

Role of the lower triplet state in photoreactions of aromatic amines

Cited by 7 publications

References 8 publications

Photodissociation ofN-Arylmethylanilines: A Laser Flash Photolysis, Fluorescence, and Product Analysis Study1

Photodissociation ofN-Arylmethylanilines: A Laser Flash Photolysis, Fluorescence, and Product Analysis Study1

Role of the Low-Energy Excited States in the Radiolysis of Aromatic Liquids

Mechanism of the Photodissociation of 4-Diphenyl(trimethylsilyl)methyl-N,N-dimethylaniline

Contact Info

Product

Resources

About

Photodissociation ofN-Arylmethylanilines: A Laser Flash Photolysis, Fluorescence, and Product Analysis Study¹

Photodissociation ofN-Arylmethylanilines: A Laser Flash Photolysis, Fluorescence, and Product Analysis Study¹