Nitroxide reduction by electron transfer from the eosin triplet state: electron paramagnetic resonance and flash photolysis studies

Seret, Alain; Gandin, E.; Vorst, A. Van de

doi:10.1016/0047-2670(87)87013-2

Cited by 13 publications

(10 citation statements)

References 23 publications

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“…species by radical recombination and/or by quenching of the excited states of the dye. This suggests that the nitroxides could extinguish the photoinduced dehalogenation reaction (Figure b, depicting the variation of the EPR signal as a function of the irradiation time for mixture ii; see also details in Figures S49–S50, Supporting Information). Indeed, after this time lapse, a new series of signals started to appear in the EPR spectra.…”

Section: Resultsmentioning

confidence: 97%

Customizing Photoredox Properties of PXX‐based Dyes through Energy Level Rigid Shifts of Frontier Molecular Orbitals

Sciutto

Fermi

Folli

et al. 2018

Chemistry A European J

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Here we describe the synthesis of electron-rich PXX derivatives in which the energy levels of the excited states have been rigidly shifted through the insertion of imide groups. This has allowed the development of a new series of oxygen-doped photoredox-active chromophores with improved oxidizing and reducing properties. Capitalizing on the dehalogenation of organic halides as a model reaction, we could investigate the photooxidative and photoreductive potential of these molecules in model chemical transformations. Depending on the substrate, solvent and dye the reaction mechanism can follow different paths. This prompted us to consider the first chemoselective transformation protocol, in which two different C-Br bonds could be chemoselectively reacted through the sequential photoactivation of two different colorants.

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Section: Resultsmentioning

confidence: 97%

Customizing Photoredox Properties of PXX‐based Dyes through Energy Level Rigid Shifts of Frontier Molecular Orbitals

Sciutto

Fermi

Folli

et al. 2018

Chemistry A European J

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“…The formation of singlet oxygen upon irradiation of protoberberinium salts I-III was confirmed using the selective reaction of TMP with 1 O 2 (Lion et al, 1976;Seret et al, 1987;Zang et al, 1995;Brezová et al, 2003), which results in the formation of a stable nitroxyl free radical TEMPOL (Eqn (6)) (6)…”

Section: Singlet Oxygen Generationmentioning

confidence: 88%

Oxygen activation by photoexcited protoberberinium alkaloids from Mahonia aquifolium

Brezová¹,

Dvoranová²,

Kostálová³

2004

Phytotherapy Research

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Protoberberinium salts, i.e. berberine (I), palmatine (II) and jatrorrhizine (III) prepared from Mahonia aquifolium (Pursh) Nutt. belong to isoquinoline alkaloids possessing interesting biological activity (e.g. antibacterial, antimalarial, antitumor). The characteristic UV/Vis absorption band maxima of I-III iodide salts were found in regions 350 and 425 nm in dimethylsulfoxide (DMSO) and ethanol solvents, and were only negligibly influenced by substitution changes on the C-2 and C-3 positions. The fluorescence intensity of protoberberinium salts monitored in ethanol solutions was significantly lowered by iodide counter-ions, and decreased in the order berberine > palmatine > jatrorrhizine. EPR spectroscopy supplied evidence of the formation of super-oxide anion radicals and singlet oxygen upon irradiation of berberine in oxygenated DMSO solvent. The photochemical generation of O(2) (.-) and (1)O(2) in DMSO solutions of palmatine and jatrorrhizine was substantially lower, and probably reflected the replacement of a photolabile methylenedioxy group at C-2 and C-3 positions in the berberine molecule by two methoxy groups in palmatine, and methoxyl (C-2) and hydroxyl (C-3) substitution in jatrorrhizine. Additionally, the powder EPR spectra of protoberberinium iodides I-III measured at 290 K revealed the presence of single-line EPR signals (g(eff) = 2.0044), which were attributed to hydroperoxidic structures produced by the autoxidation process. The photochemical reactions of protoberbenium salts producing reactive oxygen species after UVA excitation should be integrated in biological activity investigations, as well as in their applications in skin disorder treatment.

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“…Phosphorescence [5] and delayed fluorescence [3,[6][7][8] have been observed even at room temperature. Triplet excited eosin Y has a high efficiency of singlet oxygen generation [9-11] (T+ 3 0 2 -S+ l 0 2 ; T is eosin Y in triplet state and S is eosin Y in singlet state) and it acts as photosensitizer of chemical reactions [12,13] (photosensitized oxidation [14][15][16][17][18] and photosensitized reduction [ 19,20]). …”

Section: Introductionmentioning

confidence: 99%

Triplet-triplet absorption of eosin Y in methanol determined by nanosecond excimer laser excitation and picosecond light continuum probing

Penzkofer

Beidoun

1993

Chemical Physics

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The absolute triplet-triplet absorption cross-section spectrum a T (X) of eosin Y in methanol at room temperature is determined in the wavelength region from 400 to 1000 nm and at 308 and 1054 nm. The triplet state is populated by XeCl excimer laser excitation to a singlet state and subsequent intersystem crossing. The triplet level population is determined by numerical simulation of the pump pulse absorption dynamics. The triplet-triplet absorption is probed with picosecond spectral light continua which are generated in a D 2 0 sample by a synchronized mode-locked Nd:glass laser. The decay of the triplet level population is studied by delayed picosecond light continua probing. Second order rate constants of hQ* =* i.l X10 9 dm 3 mol~l s~l for oxygen quenching, fc&> = i.3x 10 9 dm 3 mol~l s~l for triplet-triplet annihilation, and k$ ss4x 10 8 dm 3 mol~l s" 1 for triplet-singlet concentration quenching have been determined.

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Nitroxide reduction by electron transfer from the eosin triplet state: electron paramagnetic resonance and flash photolysis studies

Cited by 13 publications

References 23 publications

Customizing Photoredox Properties of PXX‐based Dyes through Energy Level Rigid Shifts of Frontier Molecular Orbitals

Customizing Photoredox Properties of PXX‐based Dyes through Energy Level Rigid Shifts of Frontier Molecular Orbitals

Oxygen activation by photoexcited protoberberinium alkaloids from Mahonia aquifolium

Triplet-triplet absorption of eosin Y in methanol determined by nanosecond excimer laser excitation and picosecond light continuum probing

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