Introduction to Dynamic Spin Chemistry

Hayashi, H.

doi:10.1142/5316

Cited by 168 publications

(172 citation statements)

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“…32 In the literature it is suggested that this difference in g factors leads to a magnetic-field-dependent mixing of the |S 0 and |T 0 states in large applied fields. It is argued that this g mechanism yields a √ B magnetic-field dependence of the recombination rate for radical pairs, 17 but it has never been explicitly shown that this dependence holds for the different OMAR models as assumed, for example, by Wang et al 7 Therefore, we will study the MC in the e-h pair model with a small difference in g factors of the electron and hole using the stochastic Liouville equation.…”

Section: G Mixingmentioning

confidence: 99%

“…Furthermore, random encounter processes are taken into account as the derivation is performed for free radicals in solution. This means that although many successful models for magnetic-field-dependent reactions have been introduced in spin chemistry, 17 one has to be careful with naively applying them to OMAR. (ii) The linewidth is solely determined by the exchange interaction and the difference between the g factors.…”

Section: G Mixingmentioning

confidence: 99%

“…(17). To calculate the magnetic-field dependence of T-T annihilation the following stochastic Liouville equation is used:…”

Section: Triplet-triplet Annihilationmentioning

confidence: 99%

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Microscopic modeling of magnetic-field effects on charge transport in organic semiconductors

et al. 2011

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The stochastic Liouville equation is applied to the field of organic magnetoresistance to perform detailed microscopic calculations on the different proposed models. By adapting this equation, the influence of a magnetic field on the current in bipolaron, electron-hole pair, and triplet models is calculated. The simplicity and wide applicability of the stochastic Liouville equation makes it a powerful tool for interpreting experimental results on magnetoresistance measurements in organic semiconductors. New insights are gained on the influence of hopping rates and disorder on the magnetoresistance.

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Section: G Mixingmentioning

confidence: 99%

Section: G Mixingmentioning

confidence: 99%

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Microscopic modeling of magnetic-field effects on charge transport in organic semiconductors

et al. 2011

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“…[1][2][3] Magnetic fields interact with the electron spins of RPs, and thus the spin conversion in the RPs is influenced by the fields. The lifetime of the RPs and the yield of the escaped radicals consequently show appreciable MFEs.…”

Section: Introductionmentioning

confidence: 99%

Magnetic Field Effect on a Radical Pair Reaction as a Probe of Microviscosity

2008

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The magnetic field effects (MFEs), caused by the ∆g mechanism, on the photoinduced hydrogen abstraction reaction of benzopheneone with thiophenol were investigated in alcoholic solutions of varying viscosities (η ) 0.55 to 59.2 cP) by a nanosecond laser flash photolysis technique. The escape yield of benzophenone ketyl radicals (Y) gradually decreased with increasing magnetic field strength (B) from 0 to 1.6 T. The relative yield observed at 1.6 T, R(1.6 T) ) Y(1.6 T)/Y(0 T), decreased with increasing η in the range of 0.55 cP e η e 5 cP, and then increased with increasing η in the range of 5 cP < η e 55.3 cP. When η was higher than 55.3 cP, the R(1.6 T) value became 1.0, and MFEs were completely quenched. The observed η dependence of the MFEs was analyzed by the stochastic Liouville equation (SLE), in which the effects of spin-orbit coupling by a heavy atom such as sulfur were taken into account. The observed MFEs were reproduced fairly well by the SLE analysis. The diffusion coefficients of the radicals obtained by the SLE were about three times smaller than those expected from the macroscopic solvent viscosities. One can probe the microviscosity in the vicinity of the radical pairs by observing MFEs on the present photochemical reaction system. IntroductionMagnetic field effects (MFEs) on photochemical reactions through radical pairs (RPs) and biradicals have received considerable attention during the past three decades. 1-3 Magnetic fields interact with the electron spins of RPs, and thus the spin conversion in the RPs is influenced by the fields. The lifetime of the RPs and the yield of the escaped radicals consequently show appreciable MFEs. In solution, the MFEs on the reactions of RPs have been interpreted in terms of the radical pair and triplet mechanisms (RPM and TM, respectively). According to the RPM, MFEs are observed during sequential steps as follows:(1) formation of close RPs through photochemical reactions with singlet (S) or triplet (T n , n ) 0, (1) spin multiplicity, (2) spin conversion between S and T n states in separated RPs, and (3) spin state selective recombination of the close RPs competing with the escape of radicals from the pairs. 2 These steps are promoted by the diffusion of the radicals by which the RPs are separated and re-encountered. Radical diffusion, therefore, has a pronounced effect on the magnitude of the observed MFEs. Large MFEs have been observed in confined and inhomogeneous systems such as micellar solutions, 2,3 highly viscous solutions, 4,5 nanotubes, 6 and very recently ionic liquids. 7 Molecular and radical diffusions are important processes that control chemical reactions in solutions. 8 Radical diffusion motion has been studied with the several techniques, including transient grating (TG), 9 photochemical space intermittency, 10,11 and electron paramagnetic resonance (EPR). 12,13 These techniques provide valuable information on radical diffusion in homogeneous solutions. Using the TG technique, for example, Terazima et al. found that photochemically genera...

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“…21 The SLE analysis indicates that the main features of the observed MFEs can be explained by the ∆g mechanism 15 combined with B-dependent spin relaxations. The SLE analysis also reveals that the transverse spin relaxation (S-T 0 relaxation) contributes to the saturation of the MFEs in the region of B < 5 T, while the longitudinal spin relaxation (S-T ( , T 0 -T ( relaxation) is responsible for the MFEs observed in the region of B > 10 T. 15 These spin relaxations are caused by the large anisotropy of the g value in the phenylthiyl radical.In the simulations, the D value was somewhat arbitrary. The D value used in the simulations yielded an effective viscosity in the cage of 1 cP.…”

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confidence: 96%

Nanoscale Heterogeneous Structure of Ionic Liquid as Revealed by Magnetic Field Effects

2009

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Large magnetic field effects (MFEs) observed for photoinduced hydrogen abstraction reaction between benzophenone and thiophenol in an ionic liquid (N,N,N,-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide, TMPA TFSA) are analyzed by using the stochastic Liouville equation for the first time. The sphere cage model can well reproduce the observed MFEs and the nanoscale heterogeneous structure with a cage radius of 1.8 ( 0.3 nm, and an effective viscosity in the cage of 1-2 cP is found to be formed in TMPA TFSA. IntroductionIonic liquids (ILs) are one of the most promising new classes of solvents in green chemistry, electrochemistry, and nanochemistry. [1][2][3][4][5][6][7] Their exceptional combination of propertiessnonvolatility, noncorrosiveness, nonflammability, stability to air and moisture, and designabilitysprovides new environments for chemical reactions. Recently, some novel chemical and photochemical reactions in ILs have been reported, 7,8 which may be due to their structural heterogeneity. Although theoretical and spectroscopic studies suggest that ILs have a heterogeneous structure as a result of strong ionic interactions and the aggregation of the nonpolar parts of ionic molecules, 9-12 the details are still unclear. Thus, understanding the nature of the heterogeneity of ILs is very important. If this is clarified, ILs may supersede conventional solvents.In 2007, we studied the magnetic field effects (MFEs) on photochemical reactions in ILs and found large MFEs on the radical pair (RP) generated by the photoinduced hydrogen abstraction reaction between benzophenone (BP) and thiophenol (PhSH) in an IL of N,N,N,-trimethyl-N-propyl-ammonium bis(trifluoromethanesulfonyl) amide (TMPA TFSA). 13 In the previous paper, we suggested a cage effect caused by the heterogeneity of the IL as a qualitative explanation for such large MFEs on the RP. In RPs generated by photochemical reactions, the unpaired electron spins on each radical are coupled, giving two different spin states: singlet (S) and triplet (T). According to the Pauli principle, singlet RPs can react to form a recombination product, whereas triplet RPs cannot react in each other but form an escaped radical. Magnetic fields interact with these spins and affect the reaction of the RPs without changing other parameters such as the reaction rate of singlet RPs, activation barrier, and diffusion motion of the radicals. Since the interaction between magnetic fields and spins can be described by quantum chemistry, MFE studies on RPs provide valuable information on their kinetics and dynamics, and in particular on aspects of the environment around RPs such as heterogeneity, domain, and cage size. 14,15 In this paper, we describe the first numerical analysis of the MFEs observed in the IL by using the stochastic Liouville equation (SLE). Here, we report that the sphere cage model can well reproduce the observed MFEs and the nanoscale heterogeneous structure with a cage radius (R) of 1.8 ( 0.3 nm and an effective viscosity (η) in the cage of 1-2 ...

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Introduction to Dynamic Spin Chemistry

Cited by 168 publications

References 0 publications

Microscopic modeling of magnetic-field effects on charge transport in organic semiconductors

Microscopic modeling of magnetic-field effects on charge transport in organic semiconductors

Magnetic Field Effect on a Radical Pair Reaction as a Probe of Microviscosity

Nanoscale Heterogeneous Structure of Ionic Liquid as Revealed by Magnetic Field Effects

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