Conical Intersections in Charge-Transfer Induced Quenching

Sinicropi, Adalgisa; Pischel, Uwe; Basosi, Riccardo; Nau, Werner M.; Olivucci, Massimo

doi:10.1002/1521-3773(20001215)39:24<4582::aid-anie4582>3.0.co;2-4

Cited by 41 publications

(73 citation statements)

References 26 publications

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“…The intriguing photophysics of fluorazophores has been worked out in great detail [6][7][8][9][10][11] and the fascinating quenching pathways have been investigated through a combination of experimental and theoretical methods [12][13][14]. On the more applied side, fluorazophores have proven to be useful as sensors for antioxidant activity, both in solution [15][16] as well as in membrane-mimetic systems [17], as probes for measuring the kinetics of association with supramolecular systems [18] [19], as tools to investigate the geometries of cyclodextrin inclusion complexes by means of circular dichroism [20] [21], and as probes for the polarizability inside molecular container molecules [22].…”

Section: Methodsmentioning

confidence: 99%

“…probe and quencher must come into van-der-Waals contact (2-3 Å distance) for quenching to occur. This is naturally fulfilled for quenching by hydrogen atom transfer or exciplexinduced quenching, which are the two prototypal quenching mechanisms of the DBO chromophore [3][6][8] [13][14] [37][38][39]. However, quenching by electron transfer, which presents an alternative quenching mechanism, could operate through bond (superexchange mechanism); it could also occur over a considerable distance through space or through the solvent (up to 5-8 Å) and must therefore be excluded [40].…”

Section: Methodsmentioning

confidence: 99%

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Exploiting Long-Lived Molecular Fluorescence

Nau¹,

Huang²,

Wang³

et al. 2003

Chimia

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Fluorophores based on the azo chromophore 2,3-diazabicyclo[2.2.2]oct-2-ene, referred to as fluorazophores, display an exceedingly long fluorescence lifetime. Besides the use in time-resolved screening assays, where the long-lived fluorescence can be time-gated, thereby improving the signal to background ratio, a distinct application of fluorazophores lies in the area of biopolymer dynamics. For this purpose, one chain end is labeled with a fluorazophore and the other one with an efficient fluorescence quencher. The fluorescence lifetime of the probe/quencher-labeled peptide then reflects the kinetics of intramolecular endto-end collision. Applications to polypeptides are described and control experiments which establish the nature of the quenching mechanism as a diffusive process requiring intimate probe/quencher contact are described.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Exploiting Long-Lived Molecular Fluorescence

Nau¹,

Huang²,

Wang³

et al. 2003

Chimia

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“…Sinicropi et al. (46) studied the intermolecular electron and proton transfer between amine and electronically excited azoalkane. More recently, Frutos et al.…”

Section: Introductionmentioning

confidence: 99%

Photoreaction in BLUF Receptors: Proton‐coupled Electron Transfer in the Flavin‐Gln‐Tyr System^†

Udvarhelyi

Domratcheva

2011

Photochem & Photobiology

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Photoinduced electron transfer from tyrosine to the flavin chromophore is involved in activation of BLUF (sensor of blue light using FAD) photoreceptors. We studied the electron transfer (ET) coupled with proton-transfer (PT) reactions, by means of XMCQDPT2//CASSCF calculations on a molecular cluster model. By defining a minimum active space in the CASSCF calculations, we could compute the entire photoreaction pathway. We find that the crossing of the locally excited and ET states is located along the flavin bond-stretching coordinate. The ET state is stabilized by a proton transfer from the electron donor to the electron acceptor. We mapped two different PT pathways from tyrosine to flavin via the conserved glutamine. These reactions generate a tautomeric form of glutamine. Along the PT coordinates, we find geometries where the ET and the electronic ground states degenerate. At the state crossing structures, either formation of the ground state biradical intermediate or a relaxation back to the Franck-Condon minimum takes places. The computed relaxation pathways reveal that the hydrogen bonds involving glutamine in the chromophore-binding pocket control BLUF photoefficiency.

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“…In an effort to investigate polar and stereoelectronic effects on the transition state for hydrogen atom abstraction by DBO we therefore reasoned that the fluorescence quenching of DBO by phenols and alkylbenzenes could provide a model reaction for a "pure" photoinduced hydrogen abstraction devoid of complications caused by competitive exciplex formation as for excited ketones. Although numerous experimental and theoretical studies on the fluorescence quenching of DBO have been reported (9,(16)(17)(18)29,(31)(32)(33)(34)(35), none of them dealt with polar effects or a series of aromatic quenchers (except for some dihydroxyindoles [36] and electron-donating anilines [ 171) to allow a comparison with the large amount of data available for excited ketones. It should be stressed that the understanding of the electronic requirements of hydrogen transfer reactions from aromatic molecules is most relevant to biological problems.…”

Section: Introductionmentioning

confidence: 99%

Investigation of Polar and Stereoelectronic Effects on Pure Excited-state Hydrogen Atom Abstractions from Phenols and Alkylbenzenes†

Pischel

Patra

Koner

et al. 2006

Photochem Photobiol

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The fluorescence quenching of singlet-excited 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by 22 phenols and 12 alkylbenzenes has been investigated. Quenching rate constants in acetonitrile are in the range of 10(8)-10(9) M(-1)s(-1) for phenols and 10(5)-10(6) M(-1)s(-1) for alkylbenzenes. In contrast to the quenching of triplet-excited benzophenone, no exciplexes are involved, so that a pure hydrogen atom transfer is proposed as quenching mechanism. This is supported by (1) pronounced deuterium isotope effects (kH/kD ca 4-6), which were observed for phenols and alkylbenzenes, and (2) a strongly endergonic thermodynamics for charge transfer processes (electron transfer, exciplex formation). In the case of phenols, linear free energy relationships applied, which led to a reaction constant of rho = -0.40, suggesting a lower electrophilicity of singlet-excited DBO than that of triplet-excited ketones and alkoxyl radicals. The reactivity of singlet-excited DBO exposes statistical, steric, polar and stereoelectronic effects on the hydrogen atom abstraction process in the absence of complications because of competitive exciplex formation.

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Conical Intersections in Charge-Transfer Induced Quenching

Cited by 41 publications

References 26 publications

Exploiting Long-Lived Molecular Fluorescence

Exploiting Long-Lived Molecular Fluorescence

Photoreaction in BLUF Receptors: Proton‐coupled Electron Transfer in the Flavin‐Gln‐Tyr System^†

Investigation of Polar and Stereoelectronic Effects on Pure Excited-state Hydrogen Atom Abstractions from Phenols and Alkylbenzenes†

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Conical Intersections in Charge-Transfer Induced Quenching

Cited by 41 publications

References 26 publications

Exploiting Long-Lived Molecular Fluorescence

Exploiting Long-Lived Molecular Fluorescence

Photoreaction in BLUF Receptors: Proton‐coupled Electron Transfer in the Flavin‐Gln‐Tyr System†

Investigation of Polar and Stereoelectronic Effects on Pure Excited-state Hydrogen Atom Abstractions from Phenols and Alkylbenzenes†

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Product

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Photoreaction in BLUF Receptors: Proton‐coupled Electron Transfer in the Flavin‐Gln‐Tyr System^†