Magnetic field effects in radical pair recombination. II. Spin exchange relaxation and CIDN(E)P in bulk recombination

Shushin, A. I.

doi:10.1016/0301-0104(90)80086-d

Cited by 28 publications

(13 citation statements)

References 20 publications

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“…In a nonconjugated nitroxide biradical, a magnitude of J RR mainly depends on direct overlap between orbitals of unpaired electrons and/or on spin polarization via σ bonds − where r is the inter-radical distance and J 0 is the magnitude of the exchange interaction at distance d of the closest approach with a characteristic length factor α -1 . Although several kinds of parameter sets are reported in the literatures, − J ( r ) is always calculated to be less than 1 MHz for r = 10.6 Å such that J ( r ) = 0.19 MHz for r = 10.6 Å, J 0 = 10 13 s -1 , α = 2.5 Å -1 , and d = 3.5 Å .…”

Section: Discussionmentioning

confidence: 99%

“…J RR due to the direct overlap is approximated by an exponential function J ( r ) = J 0 e -α( r - d ) , − where r is the inter-radical distance and J 0 is the magnitude of the exchange interaction at distance d of the closest approach with a characteristic length factor α -1 . Although several kinds of parameter sets are reported in the literatures, − J ( r ) is always calculated to be less than 1 MHz for r = 10.6 Å such that J ( r ) = 0.19 MHz for r = 10.6 Å, J 0 = 10 13 s -1 , α = 2.5 Å -1 , and d = 3.5 Å . As for a contribution via spin polarization of the σ bonds, J RR is approximated roughly by the equation J RR = (−1) n 3 × 10 6- n MHz, where n is a number of the σ bonds.…”

Section: Discussionmentioning

confidence: 99%

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First Observation of the Photoexcited Quintet State in Fullerene Linked with Two Nitroxide Radicals

1999

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The bisadduct of fullerene (1) having two nitroxide radicals at the trans-3 position was newly synthesized. The ground and photoexcited states of 1 were studied by continuous-wave and pulsed two-dimensional electron paramagnetic resonance spectroscopy. An exchange interaction between the radicals was evaluated to be much smaller than an isotropic hyperfine splitting, showing a doublet (S = 1/2) character in the ground state. It was found from a 2D nutation spectrum that a photoexcited state has a quintet character (S = 2) which is generated via interactions between photoexcited triplet fullerene (S = 1) and the two nitroxide radicals (S = 1/2).

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

First Observation of the Photoexcited Quintet State in Fullerene Linked with Two Nitroxide Radicals

1999

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“…In eq the quenching process is quite adequately described by proper inner boundary condition ,, false[ ( r q − λ̂ q ) ∇ r boldn − boldn false] | r = r normalq = 0 , goodbreak0em1em⁣ where nobreak0em0.25em⁡ λ̂ normalq = r normalq P̂ normalD Here λ̂ q is the matrix of quenching radii in D -states of the TR -pair (see eq ).…”

Section: Methods and Approximationsmentioning

confidence: 99%

Radical–Triplet Pair Mechanism of Electron Spin Polarization. Detailed Theoretical Treatment

2014

J. Phys. Chem. A

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Specific features of net chemically induced dynamic electron spin polarization (CIDEP) P(n), generated in liquid-phase triplet-radical (TR) quenching, are analyzed in detail within the general model, which allows for fairly simple analysis of CIDEP both numerically and analytically. This model enables one to accurately treat nonadiabatic transitions between the terms of TR-pair spin Hamiltonian, resulting in CIDEP generation. The proposed theory predicts fairly simple analytical dependence of P(n) on parameters of the model. In particular, it is shown that within the wide region of parameters the P(n) dependence on the coefficient of relative TR diffusion D(r) is described by simple linear relation P(n)(-1)(D(r)) ≈ Q0 + q̅(n)D(r) (Q0 and q̅(n) are independent of D(r)). It is also demonstrated that obtained numerical and analytical results are very helpful for the analysis of experimental data, which is demonstrated by analyzing the experimental D(r)-dependence of P(n).

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“…Particularly, electron exchange interaction between the transient paramagnetic species is one of the important intermolecular interactions for the photoreaction dynamics. The exchange interaction in radical pairs has been widely studied by TR-ESR spectroscopy, ,,− and information about the exchange interaction has been obtained from the electron spin polarization generated by the RPM 25,26,35-37,39 and from TR-ESR spectra of spin-correlated radical pairs (SCRP). , Quite recently, a TR-ESR spectrum of SCRP of biradicals was analyzed based on a relaxation mechanism including the J modulation caused by conformational motion in a radical pair . Contrary to the radical pair system, there is little information about the electron exchange interaction in the system of the radical and excited triplet molecule, which is an important interaction for the photochemical dynamics in the more complex paramagnetic systems.…”

Section: Introductionmentioning

confidence: 99%

Exchange Interaction in Radical−Triplet Pairs: Evidences for CIDEP Generation by Level Crossings in Triplet−Doublet Interactions

et al. 1998

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Chemically induced dynamic electron polarization (CIDEP) generated through interaction of the excited triplet state of 1-chloronaphthalene, benzophenone, benzil, and Buckminsterfullerene (C60) with 2,2,6,6,-tetramethyl-1-piperidinyloxyl (TEMPO) radical was investigated by using time-resolved ESR spectroscopy. We carefully examined what factors affect the CIDEP intensities. By comparing CIDEP intensities of TEMPO in the 1-chloronaphthalene, benzophenone, and benzil systems with that obtained in the C60−TEMPO system, the absolute magnitude of net emissive polarization was determined to be −2.2, −6.9, and −8.0, respectively, in the units of Boltzmann polarization. In the 1-chloronaphthalene−TEMPO system, the viscosity effect on the magnitude of net polarization was studied by changing the temperature (226−275 K) in 2-propanol. The emissive polarization was concluded to result from the state mixing between quartet and doublet manifolds in a radical−triplet pair induced by the zero-field splitting interaction of the counter triplet molecule. The magnitude of net polarization is much larger than the polarization calculated with the reported theory that the CIDEP is predominantly generated in the region where the exchange interaction is smaller than the Zeeman energy. Our experimental results are quantitatively explained by the theory that the CIDEP is generated predominantly in the regions where the quartet and doublet levels cross. We propose a theoretical treatment to calculate the magnitude of net polarization generated by the level crossings in the radical−triplet pair mechanism under highly viscous conditions and perform a numerical analysis of the net RTPM polarization with the stochastic-Liouville equation. The viscosity dependence of the net polarization indicates that the back transition from the doublet to quartet states sufficiently occurs in the level-crossing region under highly viscous conditions. The estimated large exchange interaction suggests that the quenching of the excited triplet molecules by TEMPO proceeds via the electron exchange interaction.

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Magnetic field effects in radical pair recombination. II. Spin exchange relaxation and CIDN(E)P in bulk recombination

Cited by 28 publications

References 20 publications

First Observation of the Photoexcited Quintet State in Fullerene Linked with Two Nitroxide Radicals

First Observation of the Photoexcited Quintet State in Fullerene Linked with Two Nitroxide Radicals

Radical–Triplet Pair Mechanism of Electron Spin Polarization. Detailed Theoretical Treatment

Exchange Interaction in Radical−Triplet Pairs: Evidences for CIDEP Generation by Level Crossings in Triplet−Doublet Interactions

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