Spin polarization generated in the triplet-doublet interaction: hyperfine-dependent chemically induced dynamic electron polarization

Kawai, Akio; Okutsu, Tetsuo; Obi, Kinichi

doi:10.1021/j100176a020

Cited by 161 publications

(151 citation statements)

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“…Interestingly, the experimental CIDEP pattern for the C 60 -isopropyl radical can be reproduced reasonably well if CIDEP is calculated for a pair of radicals with the fictitious S ) 1 / 2 radical with no magnetic nuclei and with the g-factor equal to that of the C 60 triplet, using the conventional Q 1/2 intensity dependence used for normal radical pairs. 21 This Q 1/2 calculation was shown to be justified for a pair involving a C 60 triplet. 21 Greater agreement can be achieved if one takes into account the different line widths for the different hyperfine components.…”

Section: Radicals Produced By Photolysis Of the Corresponding Dimersmentioning

confidence: 85%

“…21 This Q 1/2 calculation was shown to be justified for a pair involving a C 60 triplet. 21 Greater agreement can be achieved if one takes into account the different line widths for the different hyperfine components. When C 60 triplets are involved, it is likely that the mixing of states is caused not by the dipolar interaction in the molecular triplet (as ZFS parameters D and E are relatively small for the C 60 triplet), but rather by the HFC and ∆g interactions.…”

Section: Radicals Produced By Photolysis Of the Corresponding Dimersmentioning

confidence: 85%

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CIDEP Studies of Fullerene-Derived Radical Adducts

Koptyug¹,

Goloshevsky²,

Zavarine³

et al. 2000

J. Phys. Chem. A

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Photolyses of solutions containing organomercury compounds (HgR 2 ) in the presence of C 60 fullerene have been investigated by Fourier transform time-resolved EPR (FT TR EPR) and continuous-wave EPR (CW EPR) techniques. By FT TR EPR, both electron-spin-polarized 3 C 60 (A polarization) and electron-spin-polarized adducts • C 60 R (E/A + E polarization) are observed. The CW EPR spectra of the • C 60 R radicals under steadystate irradiation also exhibit some electron-spin polarization. The chemically induced dynamic electron polarization (CIDEP) in the FT TR EPR experiments is explained by the following series of steps. Photolysis initially causes cleavage of the organomercury compounds into radicals that add to C 60 to form • C 60 R. The latter combine to form the dimers, [C 60 R] 2 , which are thermally stable and accumulate in the samples. In all of the reported experiments, a certain quantity of dimers is produced by photolysis before the EPR spectra are acquired. In the FT TR EPR experiments, laser excitation produces 3 C 60 by excitation of C 60 and • C 60 R by photocleavage of the dimers. The observed E/A CIDEP patterns at short (<1 µs) delays after the laser flash are proposed to be a result of the creation of polarization through the radical-pair mechanism (RPM) resulting from the interactions of two• C 60 R radicals (geminate or free) formed from the photocleavage of [C 60 R] 2 dimers. The additional E polarization observed at later times (>1 µs) is proposed to result from the interaction of 3 C 60 with • C 60 R radicals, creating E polarization through the radical-pair-triplet mechanism (RPTM). The polarization observed in the CW EPR experiments is attributed to the maintenance of polarization through the radical lifetime because of the extremely long spin-lattice relaxation of the • C 60 R radicals. The latter conclusion is consistent with the very small (50 mG) line widths of the adduct radicals. An upper limit for the bond energy of the [C 60 R] 2 dimers of 226 kJ/mol is established by the observation of the CIDEP of • C 60 R radicals when 532-nm excitation is employed. The role of multiple adducts in the observed FT TR EPR spectra is discussed.

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Section: Radicals Produced By Photolysis Of the Corresponding Dimersmentioning

confidence: 85%

Section: Radicals Produced By Photolysis Of the Corresponding Dimersmentioning

confidence: 85%

CIDEP Studies of Fullerene-Derived Radical Adducts

Koptyug¹,

Goloshevsky²,

Zavarine³

et al. 2000

J. Phys. Chem. A

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“…This phenomenon depends on the radical hyperfine component and produces a line intensity multiplet effect. 6 For a nitroxide radical-triplet pair, if the g factors of the two partners do not differ appreciably, the central 14 N hyperfine component of the nitroxide three line spectrum results to be unpolarized while the external components are polarized with opposite phase.…”

Section: Cidep Generation By Rtpmmentioning

confidence: 99%

“…3 The triplet excitation is known to be quenched by the presence of free radicals and paramagnetic impurities. 4 About ten years ago it was realized that the spin sublevels of the radicals involved in triplet quenching become spin polarized, [5][6][7] i.e., with their populations deviating from the Boltzmann equilibrium values. This effect is observed in the electron paramagnetic resonance (EPR) spectrum of the free radicals, which displays lines in enhanced absorption (A) or even in emission (E), when they are in the presence of a photoexcited triplet molecule.…”

Section: Introductionmentioning

confidence: 99%

Interaction between TOAC free radical and photoexcited triplet chromophores linked to peptide templates

Corvaja¹,

Sartori²,

Toffoletti³

et al. 2000

Biopolymers

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“…The radical-triplet pair mechanism (RTPM) is the standard mechanistic description. [1][2][3][4][5][6][7][8] Equations 1-10 represent a series of elementary steps that have been proposed to explain the CIDEP that is observed when anthracene is photoexcited in air-saturated solutions containing nitroxides. In the absence of oxygen, when triplet anthracene molecules are quenched by a nitroxide molecule, net emissive TR-EPR signals of the nitroxide are expected (eq 5).…”

Section: Introductionmentioning

confidence: 99%

Chemically Induced Dynamic Electron Polarization Generated through the Interaction between Singlet Molecular Oxygen and Nitroxide Radicals

et al. 2005

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An absorptive chemically induced dynamic electron polarization (CIDEP) was generated by the quenching of singlet oxygen by nitroxide radicals (TEMPO derivatives). The spin polarization decay time of the nitroxide (measured by time-resolved EPR) correlates with the lifetime of singlet oxygen (measured by singlet oxygen phosphorescence spectroscopy). In addition, a deuterium isotope effect on the spin polarization decay time was observed, a signature of singlet oxygen involvement. With use of isotope labeled nitroxides ( 15 N, 14 N), the relative spin polarization efficiencies of TEMPO, 4-oxo-TEMPO, and 4-hydroxy-TEMPO by singlet oxygen were determined. The relative spin polarization efficiencies (per quenching event) decrease in the order 4-hydroxy-TEMPO > TEMPO > 4-oxo-TEMPO, whereas an opposite trend was observed for the total quenching rate constants of singlet oxygen by the nitroxides where the order is 4-hydroxy-TEMPO < TEMPO < 4-oxo-TEMPO.

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Spin polarization generated in the triplet-doublet interaction: hyperfine-dependent chemically induced dynamic electron polarization

Cited by 161 publications

References 0 publications

CIDEP Studies of Fullerene-Derived Radical Adducts

CIDEP Studies of Fullerene-Derived Radical Adducts

Interaction between TOAC free radical and photoexcited triplet chromophores linked to peptide templates

Chemically Induced Dynamic Electron Polarization Generated through the Interaction between Singlet Molecular Oxygen and Nitroxide Radicals

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