Diffusion affected magnetic field effect in exciplex fluorescence

Burshteǐn, A. I.; Ivanov, Anatoly I.

doi:10.1063/1.4886809

Cited by 8 publications

(5 citation statements)

References 27 publications

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“…To calculate the recombination rate constant, we used the so-called Encounter theory [ 35 , 37 , 43 , 45 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 ], which is a generalization of the theory of diffusion-influenced reactions in the liquid phase for reactions of reactants with an internal quantum, particularly spin structure. In this theory, the equations for the

and

density matrices, which are normalized to radical concentrations, have the following general form:

…”

Section: Resultsmentioning

confidence: 99%

Magnetic Field Effect in Bimolecular Rate Constant of Radical Recombination

Doktorov

Lukzen

2023

IJMS

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The influence of magnetic fields on chemical reactions, including biological ones, has been and still is a topical subject in the field of scientific research. Experimentally discovered and theoretically substantiated magnetic and spin effects in chemical radical reactions form the basis of research in the field of spin chemistry. In the present work, the effect of a magnetic field on the rate constant of the bimolecular spin-selective recombination of radicals in the bulk of a solution is considered theoretically for the first time, taking into account the hyperfine interaction of radical spins with their magnetic nuclei. In addition, the paramagnetic relaxation of unpaired spins of the radicals and the non-equality of their g-factors that also influence the recombination process are taken into account. It is found that the reaction rate constant can vary in magnetic field from a few to half a dozen percent, depending on the relative diffusion coefficient of radicals, which is determined by the solution viscosity. It is shown that the consideration of hyperfine interactions gives rise to the presence of resonances in the dependence of the rate constant on the magnetic field. The magnitudes of the magnetic fields of these resonances are determined by the hyperfine coupling constants and difference in the g-factors of the recombining radicals. Analytical expressions for the reaction rate constant of the bulk recombination for magnetic fields larger than hfi (hyperfine interaction) constants are obtained. In general, it is shown for the first time that accounting for hyperfine interactions of radical spins with magnetic nuclei significantly affects the dependence of the reaction rate constant of the bulk radical recombination on the magnetic field.

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and

density matrices, which are normalized to radical concentrations, have the following general form:

…”

Section: Resultsmentioning

confidence: 99%

Magnetic Field Effect in Bimolecular Rate Constant of Radical Recombination

Doktorov

Lukzen

2023

IJMS

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“…This potential was calculated following an approach based on the D – E 0 theorem as outlined in refs and . Note that more elaborate schemes of treating the diffusion-influenced reversible exciplex kinetics have been derived on the basis of the integral encounter theory. − While also comprehensively applicable to highly viscous mixtures, this approach is difficult to employ for radical pairs with a multitude of magnetic nuclei (as is the case here) and beyond the scope of the current presentation. Figure illustrates the microheterogeneous medium structure to clarify typical length scales and the extent of the local enrichment of the polar component as predicted on the basis of the continuum model from ref .…”

Section: Methodsmentioning

confidence: 99%

Effects of Preferential Solvation Revealed by Time-Resolved Magnetic Field Effects

et al. 2017

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External magnetic fields can impact recombination yields of photoinduced electron transfer reactions by affecting the spin dynamics in transient, spin-correlated radical pair intermediates. For exciplex-forming donor–acceptor systems, this magnetic field effect (MFE) can be investigated sensitively by studying the delayed recombination fluorescence. Here, we investigate the effect of preferential solvation in microheterogeneous solvent mixtures on the radical pair dynamics of the system 9,10-dimethylanthracene (fluorophore)/N,N-dimethylaniline (quencher) by means of time-resolved magnetic field effect (TR-MFE) measurements, wherein the exciplex emission is recorded in the absence and the presence of an external magnetic field using time-correlated single photon counting (TCSPC). In microheterogeneous environments, the MFE of the exciplex emission occurs on a faster time scale than in iso-dielectric homogeneous solvents. In addition, the local polarity reported by the exciplex is enhanced compared to homogeneous solvent mixtures of the same macroscopic permittivity. Detailed analyses of the TR-MFE reveal that the quenching reaction directly yielding the radical ion pair is favored in microheterogeneous environments. This is in stark contrast to homogeneous media, for which the MFE predominantly involves direct formation of the exciplex, its subsequent dissociation to the magneto-sensitive radical pair, and re-encounters. These observations provide evidence for polar microdomains and enhanced caging, which are shown to have a significant impact on the reaction dynamics in microheterogeneous binary solvents.

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“…This condition is fulfilled when the equation η e = (1 – η f )/2 is met. From this equation and eq for k t = k c = 0 and k s = 0 we obtain k normalD = k normala μ 0 ( τ e k d − 1 ) This equation provides a rough estimation for the position of the MFE maximum. It should be noted that the bell-shaped curves are qualitatively similar to those obtained experimentally (see Figure 5 in ref ).…”

Section: Simulations Of the Magnetic Field Effectmentioning

confidence: 99%

“…Supposing the RIP and the exciplex formation proceed in accordance with the Scheme I, a theory of MFE on both the fluorophore and the exciplex is developed in refs − based on the models of incoherent and coherent spin evolution in RIPs. The reaction kinetics are described in terms of the integral encounter theory (IET) that unlike the differential encounter theory and its extension unified theory is capable of dealing with the reversible reactions. − The theory − describes well the experimentally observed dependence of MFE magnitude on both the fluorophore and exciplex fluorescence on dielectric permittivity and viscosity of the solvent. ,, …”

Section: Introductionmentioning

confidence: 99%

Magnetic Field Effects in Fluorescence of Exciplex and Fluorophore for the Weller Schemes I and II: Similarities and Differences

2014

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In exciplex-forming donor–acceptor systems the photoexcited acceptor state can be quenched either by exciplex formation at the contact of the acceptor and the donor, followed by reversible dissociation to the radical-ion pair (Scheme I), or by distant electron transfer yielding a radical-ion pair that can reversibly recombine to produce an exciplex (Scheme II). The fluorescence of the photoexcited electron acceptor (fluorophore) and the exciplex is known to be sensitive to the magnetic field, assisting spin conversion in the resulting geminate radical-ion pair (RIP). An increase of the fluorescence yield in high magnetic fields compared to low fields is known as the magnetic field effect (MFE). In this paper theories of the MFE on both the fluorophore and the exciplex within the Schemes I and II are developed. Kinetics of the reversible reactions are described in terms of the integral encounter theory that unlike the differential encounter theory is capable of dealing with such reactions. Regions of the parameters where MFE is observable are discussed. Comparison of functional dependencies of MFE on the model parameters for the Schemes I and II is carried out. Magnitudes and dependencies of MFE on the model parameters are found to be very similar for the Schemes I and II, except the dependencies of the fluorophore and exciplex MFEs on the rate constant of exciplex production from the radical-ion pair, which appear to be opposite for the Schemes I and II.

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Diffusion affected magnetic field effect in exciplex fluorescence

Cited by 8 publications

References 27 publications

Magnetic Field Effect in Bimolecular Rate Constant of Radical Recombination

Magnetic Field Effect in Bimolecular Rate Constant of Radical Recombination

Effects of Preferential Solvation Revealed by Time-Resolved Magnetic Field Effects

Magnetic Field Effects in Fluorescence of Exciplex and Fluorophore for the Weller Schemes I and II: Similarities and Differences

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