Photochemistry of radicals and biradicals

Johnston, Linda J.

doi:10.1021/cr00017a012

Cited by 69 publications

(75 citation statements)

References 40 publications

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“…24 Likewise, the ketyl radicals derived from benzophenone are known to fluoresce in liquid solution at 298 K. decay channel once enough vibrational energy is available. 19,22 Hence, the fluorescence lifetime at 77 K, where this channel is suppressed, amounts to 1.4 ms for the np D 1 excited state. 22 The appearance of the anion and cation emission bands at l f = 590 and 560 nm, respectively, upon UV irradiation of solutions of galvinoxyl has been ascribed to photoinduced disproportionation.…”

Section: Introductionmentioning

confidence: 99%

“…This is in contrast to, for example, the structurally similar diphenylmethyl type radicals, many of which emit around B550 nm (2.3 eV) in room temperature solution. 19,21 The diphenylmethyl radical itself has a temperature-independent and remarkably long excited-state lifetime of 260 ns 22 and a high fluorescence quantum yield (F f = 0.3). 23 This long lifetime is explained by the dipole forbidden character of the lowest transition reflected by a very low molar absorption coefficient.…”

Section: Introductionmentioning

confidence: 99%

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Photophysics of the galvinoxyl free radical revisited

Grilj

Zonca

Daku

et al. 2012

Phys. Chem. Chem. Phys.

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The photophysical properties of the free neutral radical galvinoxyl were studied by a combination of femtosecond time-resolved spectroscopy and quantum chemical calculations. The electronic absorption spectrum is dominated by an intense band at 430 nm that is ascribed to the D 9,10 ' D 0 transitions. Upon photoexcitation at 400 nm, the population of the D 9,10 states decays within less than 200 fs to the electronic ground state. This ultrafast internal conversion does not involve intramolecular modes with large amplitude motion as the measured dynamics does not show any significant dependence on the environment, but is most probably facilitated by a high density of electronic states of different character. Depending on the solvent, a weak transient band due to the galvinoxylate anion is also observed. This closed-shell species, which is fluorescent although its deactivation is also dominated by non-radiative decay, is generated upon biphotonic ionization of the solvent and electron capture. The ultrashort excited-state lifetime of the galvinoxyl radical precludes photoinduced disproportionation previously claimed to be at the origin of the formation of both anion and cation.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Photophysics of the galvinoxyl free radical revisited

Grilj

Zonca

Daku

et al. 2012

Phys. Chem. Chem. Phys.

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“…[2,3] The lowest-energy triplet state of a biradical, the same source adds, lies below or at most only a little above its lowest singlet state. [4,5] Biradicals have been identified as transient intermediates in photocycloaddition reactions, [5,6] a fact that makes their isolation difficult. [4,5] Biradicals have been identified as transient intermediates in photocycloaddition reactions, [5,6] a fact that makes their isolation difficult.…”

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confidence: 99%

Unusual Inorganic Biradicals: A Theoretical Analysis

Miliordos,

Ruedenberg,

Xantheas

2013

Angewandte Chemie

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Der Biradikal‐Charakter β (mit 1 für ein ideales Biradikal) wird aus Multireferenz‐Konfigurationswechselwirkungs(MRCI)‐Wellenfunktionen bestimmt. Für die dreiatomigen Ionen der Reihe FX2+ (X=O, S, Se, Te, Po) ergeben sich mit 0.76–0.92 die höchsten β‐Werte unter den homologen 18‐Valenzelektronen‐Molekülen, verglichen mit CX22−, NX2−, X3 und OX2. Auf derselben Skala beträgt der Biradikal‐Charakter von O3 lediglich 0.19, C(CH2)3 erreicht hingegen einen Wert von 0.97.

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“…1 This is because carbon, oxygen, or nitrogen-centered radicals are generally highly reactive and their rather short ground-state lifetimes invariably preclude an in-depth spectroscopic analysis of their photoinduced processes. 1 This is because carbon, oxygen, or nitrogen-centered radicals are generally highly reactive and their rather short ground-state lifetimes invariably preclude an in-depth spectroscopic analysis of their photoinduced processes.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast primary processes of the stable neutral organic radical, 1,3,5-triphenylverdazyl, in liquid solution

Weinert

Wezisla

Lindner

et al. 2015

Phys. Chem. Chem. Phys.

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Femtosecond spectroscopy with hyperspectral white-light detection was used to elucidate the ultrafast primary processes of the thermodynamically stable organic radical, 1,3,5-triphenylverdazyl, in liquid acetonitrile solution at room temperature. The radical was excited with optical pulses having a duration of 39 fs and a center wavelength of 800 nm thereby accessing its energetically lowest electronically excited state (D1). The apparent spectrotemporal response is understood in terms of an ultrafast primary D1-to-D0 internal conversion that generates the electronic ground state of the radical in a highly vibrationally excited fashion within a few hundred femtoseconds. The replenished electronic ground state subsequently undergoes vibrational cooling on a time scale of a few picoseconds. The instantaneous absorption spectra of the radical derived from the femtosecond pump-probe data are analyzed within the Sulzer-Wieland formalism for calculating the electronic spectra of "hot" polyatomic molecules. The pump-probe spectra together with transient anisotropy data in the region of the D0 → D1 ground-state bleach gives evidence for an additional transient absorption that arises from a dark excited state, which gains oscillator strength with increasing vibrational excitation of the radical by virtue of vibronic coupling.

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Photochemistry of radicals and biradicals

Cited by 69 publications

References 40 publications

Photophysics of the galvinoxyl free radical revisited

Photophysics of the galvinoxyl free radical revisited

Unusual Inorganic Biradicals: A Theoretical Analysis

Ultrafast primary processes of the stable neutral organic radical, 1,3,5-triphenylverdazyl, in liquid solution

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