The relaxational mechanism of net CIDEP generation in triplet—radical quenching

Shushin, A. I.

doi:10.1016/0009-2614(93)89057-o

Cited by 60 publications

(85 citation statements)

References 7 publications

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“…In FPNOs the spin sublevels Q*~/2 are seleetively populated and the EPR transition is strongly polarized by the Radical Triplet Pair Mechanism (RTPM) [10][11][12]. We have observed with FPNOs two opposite types of spin polarization: emission, immediately after the LASER pulse, which reverts to enhanced absorption at longer times (e/a in the time scale) or enhanced absorption followed by emission (a/e).…”

Section: Introductionmentioning

confidence: 78%

Spin polarization and photoinduced electron transfer between ferrocene and fullerene derivatives containing a nitroxide group

et al. 1997

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Fulleropyrrolidine derivatives containing a TEMPO group (FPNOs) are examined in toluene solution, between 200 and 270 K, by TR-EPR spectroscopy afler LASER excitation. Signals of the ground and exeited states are observed and their time profiles are recorded. In presente of ferrocene the time pattern of the pola¡ is modified, showing the occurrence of intermoleeular electron transfer from the donor ferrocene to the excited FPNOs. The rate constant k~r is obtained from the simulation of the EPR signal time evolution of the ground and excited states.

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Section: Introductionmentioning

confidence: 78%

Spin polarization and photoinduced electron transfer between ferrocene and fullerene derivatives containing a nitroxide group

et al. 1997

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“…Equations (29) show that for the typical case gR ~ gT the triplet and radical spins are polarized oppositely, the net polarization sign coincides with the sign of the triplet spin polarization:…”

Section: Perturbation Theory Calculationsmentioning

confidence: 99%

“…(29) and (30) the RTPM of the spin polarization arising from the triplet quenching and the EISC gives the important result: the triplet spin is potarized one order of magnitude higher than the radicaI spin. Later the triplet polarization can be transferred to the radicals.…”

Section: Perturbation Theory Calculationsmentioning

confidence: 99%

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Time-resolved EPR study of electron spin polarization and spin exchange in mixed solutions of porphyrin stable free radicals

et al. 2003

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The time-resolved electron paramagnetic resonance (EPR) spectra are studied in the temperature range of 110-300 K for two mixed solutions of porphyrins, ZnTPP and H2TPP, in toluene and the stable free radical 2,2,6,6-tetramethyl-l-piperidinyloxyl (TEMPO). The EPR spectra and their kinetic behavior were studied for concentrations of TEMPO vafied in the interval from 0.51 to 7.68 mM, while the porphyrin concentration was fixed as I mM. The EPR spectra of triplet-state porphyrins and free radicals manifest the chemically induced spin polarization. For the relatively short-lived radical-triplet pairs, with the perturbation theory up to the fourth order, the theoretical expressions ate obtained for the triplet and radical spin polarization induced by the enhanced intersystem crossing (ISC) due to the interaction of excited singlet-state porphyrins with free radicals and by the triplet quenching by free radicals. The time-dependent EPR spectra of the t¡ are simulated taking into account the spin-lattice relaxation. Ir is shown that the variation of the triplet EPR spectra shape, when the time of observation increases, arises from the spin-lattiee relaxation kineties. The kinetic behavior of the TEMPO EPR spectrum was simulated on the basis of the kinetie scheme suggested earlier in the literature. The triplet spin-lattice relaxation time, the tate of the ISC and the lifetime of the excited singlet state were estimated by fitting the kinetic curves for the triplet EPR spectra intensity. For the mixed porphyrin-TEMPO solutions, a possible set of the rate constants of important bimolecular proeesses were determined. For this set of parameters, it turns out that the spin polarization transfer has a smaller rate constant than the rate constant of the diffusion collisions of the triplet and radical. It appears that the rate constant of the ISC catalyzed by radieals is relatively high in the solutions close to the melting point of the solvent and in the soft-glassy state. In the triplet porphyrins the initial spin pola¡ induced by the spin-selective ISC was found to exceed the equilibrium spin polarization by up to two orders of magnitude.

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“…Current theories provide analytical [29,[35][36][37] and numerical [34] results for the dependence of the spin polarization upon the zero-field splitting (ZFS) parameter (D), solvent viscosity (Z) and radical-triplet electron spin exchange (J). According to RTPM theory, the observed net polarization, which is equal for all hyperfine lines, depends on the precursor state (photoexcited singlet or triplet) and sign of J [38][39][40][41].…”

Section: Radical-photoinduced Triplet Interaction the Radical-tripletmentioning

confidence: 99%

Triplet porphyrins as donors in intramolecular electron transfer and their intermolecular interaction with free radicals

Blank

Galili

Levanon

2001

J. Porphyrins Phthalocyanines

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Porphyrins and related compounds are basic moieties which upon photoexcitation produce paramagnetic transients important to many processes in biology, material science and light–energy conversion. This short review demonstrates the application of time-resolved EPR spectroscopy to two processes in which the photoexcited singlet and/or triplet are involved: (1) intramolecular electron transfer in photoexcited donor–acceptor systems embedded in liquid crystals, where the porphyrins are the electron donors attached to different types of acceptors; and (2) intermolecular magnetic interactions between photoexcited porphyrin triplets and free radicals. In both systems the electron spin plays an important part with regards to the route of the magnetic interactions involved.

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The relaxational mechanism of net CIDEP generation in triplet—radical quenching

Cited by 60 publications

References 7 publications

Spin polarization and photoinduced electron transfer between ferrocene and fullerene derivatives containing a nitroxide group

Spin polarization and photoinduced electron transfer between ferrocene and fullerene derivatives containing a nitroxide group

Time-resolved EPR study of electron spin polarization and spin exchange in mixed solutions of porphyrin stable free radicals

Triplet porphyrins as donors in intramolecular electron transfer and their intermolecular interaction with free radicals

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