Excited-state properties of arylmethyl radicals containing naphthyl, phenanthryl, and biphenyl moieties

Weir, D.; Johnston, Linda J.; Scaiano, J. C.

doi:10.1021/j100318a009

Cited by 36 publications

(11 citation statements)

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“…3). The shift in X , , , from 400 nm for radicals 14 and 15 to 340 nm for 16 is in line with the reported spectra for the 1-and 2-naphthylmethyl radicals, which have absorption maxima at 365 nm, whereas the (1-bromo-2-naphthy1)methyl radical has X , , , at 350 nm (25,27). The long-wavelength absorption is rather unusual since the lowest energy band in most naphthylmethyl radicals is too weak to be observed in absorption, although its fluorescence is readily detectable in various systems (24).…”

Section: Cation Yieldssupporting

confidence: 88%

Laser flash photolysis studies of the formation and reactivities of phenyl(naphthyl)methyl carbocations generated from phosphonium salt precursors

Alonso¹,

Johnston²,

Scaiano³

et al. 1992

Can. J. Chem.

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The photolysis of several substituted phenyl(naphthy1)methyl triphenylphosphonium chlorides has been examined using a combination of laser flash photolysis experiments and product studies. Both carbocation and radical intermediates have been characterized in the transient experiments, with the relative yields depending strongly on the solvent. For example, in alcohols, acetonitrile, or aqueous solvents cation formation predominates while acetonitrile/dioxane mixtures (5-10%) are required for the observation of radicals. Quantum yields for cation formation vary from 0.79 in methanol to 0.093 in 1 : 4 acetonitrile/dioxane, as measured by product studies and transient experiments, respectively. The addition of perchlorate salts leads to dramatic enhancements in the cation lifetimes; the effects are particularly pronounced for acetonitrile/dioxane mixtures where the cation yields also increase by factors of 3-4. In this case the effects are attributed primarily to replacement of chloride by perchlorate in the initial ion pairs. The combined data from both solvent and perchlorate salt effects on the cation lifetimes and yields suggest that the excited state of the phosphonium salt cleaves homolytically, followed by electron transfer within the initial radical/triphenylphosphine radical cation pair to generate carbocation, as opposed to direct heterolytic cleavage. The cation yields also indicate that back reaction to regenerate starting material, as well as product formation within the initial geminate cage, occur in some solvents. The effects of solvent and added perchlorate salts on the rate constants for reaction with nucleophiles have been examined. For example, rate constants that vary by an order of magnitude have been measured for quenching by azide ion in various aqueous acetonitrile and trifluoroethanol mixtures.Faisant appel a une combinaison d'expkriences de photolyse kclair au laser et d'ktudes des produits, on a examink la photolyse de plusieurs chlorures de phCnyl(naphty1)mkthyl triphknyl phosphonium. On a caractkrisk des intermkdiaires tant cationiques que radicalaires dans les expkriences impliquant les espkces transitoires; les rendements relatifs dependent beaucoup du solvant. Par exemple, dans les alcools, l'acktonitrile ou des solvants aqueux, il y a formation prkdominante de cations alors qu'il faut un mklange d'acktonitrile/dioxane (5-10%) pour observer des radicaux. Les rendements quantiques pour la formation des cations, tels que mesurks respectivement par des ktudes de produits et des expkriences sur les espbces transitoires, varient de 0,79 dans le mkthanol a 0,093 dans un mklange 1 : 4 d'acktonitrile/dioxane. L'addition de sels de perchlorate conduit une augmentation dramatique des temps de vie des cations; les effets sont particulibrement prononcks pour les mklanges acktonitrile/dioxane dans lesquels les rendements en cations augmentent aussi par des facteurs de 3-4. Dans ce cas, on attribue les effets principalement a une substitution du chlorure par le perchlorate dans les paires d'ions ...

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Section: Cation Yieldssupporting

confidence: 88%

Laser flash photolysis studies of the formation and reactivities of phenyl(naphthyl)methyl carbocations generated from phosphonium salt precursors

Alonso¹,

Johnston²,

Scaiano³

et al. 1992

Can. J. Chem.

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“…The 9-anthracenylmethyl radical ( 2a ) has been the subject of recent photophysical and photochemical studies. − Tokumura and Itoh 1 reported its absorption band at ca. 420 nm on 248-nm photolysis of 9-chloromethylanthracene.…”

Section: Introductionmentioning

confidence: 99%

“…420 nm on 248-nm photolysis of 9-chloromethylanthracene. 9-Anthracenylmethyl radicals ( 2a ) were reported to show a doublet−doublet fluorescence emission (λ max = 545 nm, τ F = 21 ns). , Furthermore, upon irradiation of arylmethyl derivatives with two pulsed lasers (two-color experiments), excited arylmethyl radicals and even aryl cations were detected by UV spectroscopy …”

Section: Introductionmentioning

confidence: 99%

Multiple-Photon Chemistry of 9-(Phenoxymethyl)- and 9,10-Bis(phenoxymethyl)anthracenes in the Laser-Jet: Generation, Photochemistry, and Time-Resolved Laser-Flash Spectroscopy of Anthracenylmethyl Radicals and Pulse Radiolysis of 9-(Bromomethyl)anthracene

et al. 1997

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In the high-intensity laser-jet (LJ) photolysis of 9-(phenoxymethyl)anthracene (1a) and 9,10-bis(phenoxymethyl)anthracene (1b) multiple-photon chemistry was observed. Thus, while the [4 + 4] photodimer 8a was formed as the one-photon product in the low-intensity conventional photolysis of monoether 1a, the high-intensity irradiation in the laser-jet yielded 1,2-bis(9-anthracenyl)ethane (3a), lepidopterene (4a), biplanene (5a), 9-(chloromethyl)anthracene (6a), and 9-(methoxymethyl)anthracene (7a) as main products. The product distribution depended on the solvent used: after C−O homolysis of the ether 1a, for which at least two photons are required, the resulting arylmethyl radical 2a dimerizes in benzene, in methylene chloride it engages in photoinduced electron transfer, while in methanol it undergoes photoionization. With the help of time-resolved laser-flash photolysis of the monoether 1a it was confirmed that the homolysis of the C−O bond leads to the 9-anthracenylmethyl radical 2a. The authentic radical 2a was generated independently by time-resolved pulse radiolysis and laser-flash photolysis of 9-(bromomethyl)anthracene. Analogous to the monoether 1a, the bisether 1b gave under the high intensity conditions of the laser-jet irradiation tetrabenzo[2.2]paracyclophane (3b), its photodimer (5b), 9,10-(bischloromethyl)anthracene (6b), and 9-(chloromethyl)-10-(phenoxymethyl)anthracene (9b); their distribution depended also on the solvent used. Mechanistic pathways are offered for these multiple-photon processes.

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“…The 4-biphenylmethyl radical 2 has for some time been the subject of photophysical studies. 1,2 This benzyl-type radical 2 has a strong absorption band centred at 326 nm, 2 which makes it a suitable substrate for laser-jet experiments, 3 especially at the 333 nm line available in the argon-ion laser (333, 351, 364 nm). For other well-studied arylmethyl radicals, generated upon irradiation of arylmethyl halides with pulsed lasers (two-colour experiments), photoionization to aryl cations was demonstrated by transient UV spectroscopy.…”

Section: Introductionmentioning

confidence: 99%

Multiple-photon chemistry in the laser-jet: photochemistry of the 4-biphenylmethyl radical

Adam¹,

Schneider²

1997

J. Chem. Soc., Perkin Trans. 2

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In laser-jet (LJ) photolysis (high intensity) of the ether 4-(4-benzoylphenoxymethyl)biphenyl 1 a twophoton process is observed in CCl 4 to yield 4-(chloromethyl)biphenyl 5 as product (3%), while the onephoton product is 4-biphenylaldehyde 7 (100% in conventional photolysis versus 97% in laser-jet photolysis). In ethanol, the results suggest a three-proton reaction in which 4-(ethoxymethyl)biphenyl 6 is produced in appreciable amounts (18%) in addition to the one-photon product 1,2-bis(4-biphenyl)ethane 4, the latter as the major product (82%). It is proposed that under high-intensity LJ photolysis conditions the electronically-excited 4-biphenylmethyl radical 2* is photoionized to the 4-biphenylmethyl cation 2 + and that the latter is trapped by ethanol to give the 4-biphenylmethyl ether 6.

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Excited-state properties of arylmethyl radicals containing naphthyl, phenanthryl, and biphenyl moieties

Cited by 36 publications

References 0 publications

Laser flash photolysis studies of the formation and reactivities of phenyl(naphthyl)methyl carbocations generated from phosphonium salt precursors

Laser flash photolysis studies of the formation and reactivities of phenyl(naphthyl)methyl carbocations generated from phosphonium salt precursors

Multiple-Photon Chemistry of 9-(Phenoxymethyl)- and 9,10-Bis(phenoxymethyl)anthracenes in the Laser-Jet: Generation, Photochemistry, and Time-Resolved Laser-Flash Spectroscopy of Anthracenylmethyl Radicals and Pulse Radiolysis of 9-(Bromomethyl)anthracene

Multiple-photon chemistry in the laser-jet: photochemistry of the 4-biphenylmethyl radical

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