Quenching of excited-state xanthone and thioxanthone by inorganic anions

Abdullah, Khalid A.; Kemp, Terence J.

doi:10.1039/p29850001279

Cited by 20 publications

(13 citation statements)

References 5 publications

(6 reference statements)

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“…The fluorescence quenching of organic chromophores by inorganic anions has been reported for a number of hydrocarbon and heterocyclic systems (26)(27)(28)(29)(30). In several of these studies, triplet states of the chromophores were the only products observed from singlet state quenching and provide precedence for our observations (26,30).…”

Section: Energetics and Reactive Intermediate Formationsupporting

confidence: 68%

Mechanisms of Photoinitiated Cleavage of DNA by 1,8-Naphthalimide Derivatives¶

Rogers

Abraham

Rostkowski

et al. 2007

Photochemistry and Photobiology

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Using water-soluble 1,8-naphthalimide derivatives, the mechanisms of photosensitized DNA damage have been elucidated. Specifically, a comparison of rate constants for the photoinduced relaxation of supercoiled to circular DNA, as a function of dissolved halide, oxygen and naphthalimide concentration, has been carried out. The singlet excited states of the naphthalimide derivatives were quenched by chloride, bromide and iodide. In all cases the quenching products were naphthalimide triplet states, produced by induced intersystem crossing within the collision complex. Similarly, the halides were found to quench the triplet excited state of the 1,8-naphthalimide derivatives by an electron transfer mechanism. Bimolecular rate constants were Ͻ10 5 M Ϫ1 s Ϫ1 for quenching by bromide and chloride. As expected from thermodynamic considerations quenching by iodide was 6.7 ؋ 10 9 and 8.8 ؋ 10 9 M Ϫ1 s Ϫ1 for the two 1,8-naphthalimide derivatives employed. At sufficiently high ground-state concentration self-quenching of the naphthalimide triplet excited state also occurs. The photosensitized conversion of supercoiled to circular DNA is fastest when selfquenching reactions are favored. The results suggest that, in the case of 1,8-naphthalimide derivatives, radicals derived from quenching of the triplet state by ground-state chromophores are more effective in cleaving DNA than reactive oxygen species or radicals derived from halogen atoms.

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Section: Energetics and Reactive Intermediate Formationsupporting

confidence: 68%

Mechanisms of Photoinitiated Cleavage of DNA by 1,8-Naphthalimide Derivatives¶

Rogers

Abraham

Rostkowski

et al. 2007

Photochemistry and Photobiology

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“…In our polar and hydroxylic reaction medium, the lowest triplet state of xanthone has a pp* configuration with little tendency towards hydrogen abstraction; 13 however, it can be quenched by electron transfer from a suitable donor D. [14][15][16][17][18][19] In this work, we used triethylamine and DABCO (diazabicyclo[2.2.2]octane) for that purpose. The former has the advantage that the resulting radical cation D 1 and subsequent species, e.g., a-amino alkyl radicals, are practically nonabsorbing throughout the visible and near UV, but its volatility makes it more difficult to preadjust a desired concentration and to keep it constant during a series of measurements; furthermore, a variety of secondary thermal reactions, which also involve surplus xanthone molecules in their ground state, can complicate two-pulse experiments with longer interpulse delays.…”

Section: Photoinduced Intermediate Formationmentioning

confidence: 99%

Photoionization of xanthone via its triplet state or via its radical anion

Goez

Hussein

2004

Phys. Chem. Chem. Phys.

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“…1) comparable with the rate constants determined for 9,10-dicyanoanthracene 6 and thioxanthone. 7 The configuration of the major diastereoisomer 2a was determined by NOE-spectroscopy and by comparison of the aminoalcohol 4a which resulted from the LAH-reduction of 2a with the literature-known compound. 8 The relative configuration of the two minor components were determined from the 3 J HH coupling constants of the hydrogen proximal to the azido group.…”

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confidence: 99%