High-Field Supercage Model for Radical Pair Reactions in Micelles

Abstract

An analytic expression for the escape yield of a radical pair (RP) in a micelle under high magnetic fields is derived by the supercage model. This model is a two time scale model which divides the time evolution into two consecutive stages. The short time stage describes the initial separation of the partners of the RP, and the magnetic field dependence of the recombination yield can be described by the usual radical pair theory of freely diffusing radicals. The decay of a quasi-equilibrium during the second stage is described by rate equations for the spin density matrix, which for well-defined conditions can be reduced to a set of equations for the diagonal elements of the density matrix in the basis of true eigenstates of the Hamiltonian of the free radicals. In the present work we examine the applicability of the high-field limit of this approximation, which is closely related to the kinetic approach of H. Hayashi and S. Nagakura (Bull. Chem. Soc. Jpn. 1984, 57, 322). General analytic expressions for the magnetic field and relaxation dependence of the recombination yield during the second stage and for the decay constants are derived. The decay constants derived by H. Hayashi and S. Nagakura agree with our results. We show that the contribution from the first stage is significant and how it can be included.

Magnetic Field Effect: A Tool for Identification of Spin State in a Photoinduced Electron-Transfer Reaction

“…There are many examples where it has been cited that singlet exciplex luminescence 18-23 increases even by 10% in the presence of an external MF. On the other hand, many other examples are also there, where free ion formation is enhanced in the presence of a MF from the initially formed triplet RIPs. − ,− …”

“…Therefore, if an equilibrium exists between singlet and triplet RIPs, formation of different types of products are possible. During last two decades it has been observed that the application of a low magnetic field (MF) on this ET process − has remarkable potential in identification of original spin states of the RIPs as well as in controlling the production of cage/escape products by modulating the spin states, i.e., by disturbing the existing equilibrium between the singlet and triplet states. If it is assumed that RIPs are formed initially in the singlet state, equilibrium will exist between a singlet and three degenerate triplet states.…”

TREPR spectra of micelle-confined spin correlated radical pairs: I. Molecular motion and simulations

“…The microreactor model 46 has been analyzed theoretically by Shushin, 47,48 Pedersen et al, 49,50 and Purtov et al, 51 but none of these papers predict the asymmetry of the APS spectral shape. Admittedly, our previously successful numerical simulations of the APS asymmetry themselves do not provide much physical insight into the reasons for the asymmetry.…”

Dynamics of Spin-Correlated Radical Pairs in Non-Ionic Surfactant Solutions

“…A detailed understanding of dynamic effects in magnetic resonance spectra of interacting radicals is gradually emerging from our laboratory − and several others. − Many of these studies involve the time-resolved electron paramagnetic resonance (TREPR) observation of interacting radical pairs created in micellar solution. − Micellar solubilization is convenient for restricting free radical diffusion and increasing the probability of radical encounters. When radical pairs are created using a pulsed laser and detected in a time-resolved fashion, several mechanisms of chemically induced electron spin polarization (CIDEP) can be observed: the triplet mechanism (TM), the radical pair mechanism (RPM), , and the spin-correlated radical pair mechanism (SCRP) .…”

“…A detailed understanding of dynamic effects in magnetic resonance spectra of interacting radicals is gradually emerging from our laboratory [1][2][3] and several others. [4][5][6] Many of these studies involve the time-resolved electron paramagnetic resonance (TREPR) observation of interacting radical pairs created in micellar solution. [7][8][9] Micellar solubilization is convenient for restricting free radical diffusion and increasing the probability of radical encounters.…”