Electron transfer reactions between excited diarylmethyl and triarylmethyl carbocations and aromatic donors

Azarani, A.; Berinstain, Alain; Johnston, Linda J.; Kazanis, Sophia

doi:10.1016/1010-6030(91)85014-8

Cited by 31 publications

(25 citation statements)

References 38 publications

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“…Until recently the excited states involved in these reactions were not characterized. We recently reported a detailed study of the fluorescent properties of a variety of arylmethyl carbocations and demonstrated that excited singlet xanthenyl and dibenzosuberenyl carbocations undergo efficient intermolecular reaction with aromatic donors via an electron transfer mechanism (8). Similar results have also been reported by Das and co-workers for the 9-phenylxanthenium system (9,10).…”

supporting

confidence: 74%

“…Several additional experiments were carried out in an attempt to identify X. Firstly, the lifetime of X decreased in the presence of air or oxygen (k, (02) -8 x lo9 M-' s-I); samples deaerated with oxygen showed no evidence for either X or radical 3. This is not due to reaction of the singlet cation with oxygen since it was previously demonstrated that the fluorescence lifetime of 1 is the same within experimental error in either oxygen or nitrogen-purged TFE (8). However, addition of sufficient aromatic donor (e.g., anisole) to quench >90% of the excited singlet cations does prevent the formation of both species X and the radical.…”

mentioning

confidence: 74%

“…Despite the large volume of data on the reactivities of photogenerated ground state carbocations (I), there have been relatively few investigations of the excited state behavior of these intermediates (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12). Most of the available information deals with intramolecular rearrangements such as the photo-cyclization of the triphenylmethyl cation (2) and valence isomerizations of protonated unsaturated carbonyl compounds (3,5,6) and a variety of aromatics (7).…”

mentioning

confidence: 99%

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Characterization of the triplet excited state of the phenylxanthenium carbocation

Johnston¹,

Wong²

1992

Can. J. Chem.

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. Can. J. Chem. 70, 280 (1992). The triplet excited state of the 9-phenylxanthenium cation has been observed directly by both luminescence and transient absorption techniques. The triplet-triplet absorption shows A, , , 5 300 nm and decays over a period of several microseconds in the absence of easily oxidized donors. The triplet cation reacts with 9-phenylxanthydrol and biphenyl via electron transfer to give the corresponding radical and radical cation and also reacts rapidly with both oxygen and 1,3-cyclohexadiene.

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confidence: 74%

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confidence: 74%

mentioning

confidence: 99%

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Characterization of the triplet excited state of the phenylxanthenium carbocation

Johnston¹,

Wong²

1992

Can. J. Chem.

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“…During the last two years detailed studies of the fluorescence behavior and intermolecular reactivity of di-and triarylmethyl cationsI8 and of various 9-substituted xanthenium cations' [8][9][10][11][12][13][14][15][16][17][18][19][20] have been undertaken. The reactivity of the first excited singlet state of the 9-phenylxanthenium cation toward a variety of substituted aromatic donors has been measured and shown to involve electron transfer to give 9-phenylxanthenyl radical plus the radical cation of the aromatic donor.18-20 Rapid back electron transfer provides the major decay pathway for thesinglet geminate radical/radical ion pair.…”

Section: Introductionmentioning

confidence: 99%

Electron transfer reactions of triplet 9-arylxanthenium and 9-arylthioxanthenium cations

Johnston¹,

Wong²

1993

J. Phys. Chem.

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Triplet excited states of 9-arylxanthenium and 9-arylthioxanthenium cations have been characterized using laser flash photolysis. The triplet cations absorb at -300 nm and are long-lived ( T > 5-10 ps) in the absence of electron donors. They undergo efficient electron transfer reaction with a variety of aromatic donors, including biphenyl, naphthalene, substituted benzenes, and the precursor alcohols, to give the corresponding xanthenyl or thioxanthenyl radicals and the radical cation of the aromatic donor. Both the radical and radical cations are readily detectable by transient techniques. The rate constants for electron transfer quenching of the triplet cations decrease with increasing oxidation potential of the donor, as expected from the Rehm-Weller equation. The triplet cations are somewhat poorer oxidizing agents than the singlet excited states of the same cations due to their lower excitation energy. However, the triplet cations are much more useful sensitizers in that they give substantially higher yields of cage escape from the initial geminate pair than the corresponding singlets, based on a lower limit of 25% for biphenyl radical cation formation from the triplet 9-phenylxanthenium cation.

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“…From the relationship between the zeolite A1 content and the population of generated radical cation, it appears that A1 is somehow involved in the zeolite oxidizing sites. 34 In the present work we report that cation stabilization combined with the electron acceptor ability results in the unprecedented formation of the moderately stable xanthylium (X+) 35 Measured as the relative intensities of the 1550 to 1450 cm-' bands in the pyridine IR spectra. Only 1450 cm-' Lewis band.…”

Section: Introductionmentioning

confidence: 87%

Acid Zeolites as Electron Acceptors. Generation of Xanthylium, Dibenzotropylium, and Fluorenylium Cations from Their Corresponding Hydrides through an Electron-Transfer Mechanism

Cano¹,

Corma²,

Fornés³

et al. 1995

J. Phys. Chem.

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Adsorption of xanthene (XH) and dibenzo[a,&ycloheptatriene onto large pore acid zeolites containing Bronsted sites gives rise to the formation of xanthylium (X+) and dibenzotropylium (DT+) ions, respectively. In the case of fluorene (FH) using acid Y and / 3 zeolites, the same adsorption treatment did not allow the detection of the 9-fluorenylium cation (Ft), but instead the longer-lived radical cation FH' + was identified. Interestingly, when FH was adsorbed within acid mordenite, the simultaneous presence of FIT+ and F+ was observed. Detection of FW+, together with the product distribution of the reaction of XH under electron-transfer conditions, suggests that X+, DT+, and F+ are formed from the corresponding radical cations. Concerning the nature of the zeolite oxidizing centers, it was established that formation of tricyclic carbenium ions does not take place on the nonacidic Na+ form of zeolites. By contrast, purely Bronsted zeolite HYD-W was found to be active for the generation of X+ and FIT+. On the other hand, selective neutralization of Bronsted sites with exhaustive Na+ exchange causes the deactivation of a sample in spite of the presence of unaltered residual Lewis sites.

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Electron transfer reactions between excited diarylmethyl and triarylmethyl carbocations and aromatic donors

Cited by 31 publications

References 38 publications

Characterization of the triplet excited state of the phenylxanthenium carbocation

Characterization of the triplet excited state of the phenylxanthenium carbocation

Electron transfer reactions of triplet 9-arylxanthenium and 9-arylthioxanthenium cations

Acid Zeolites as Electron Acceptors. Generation of Xanthylium, Dibenzotropylium, and Fluorenylium Cations from Their Corresponding Hydrides through an Electron-Transfer Mechanism

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