Diffusion-model analysis of effective CIDEP distance in solvent-separated radical-ion pair

The radical pair mechanism (RPM) of chemically induced dynamic electron polarization (CIDEP) is theoretically analyzed to determine what intermolecular separations (r _eff) effectively contribute to the CIDEP generated from diffusive, separated radical-ion pairs (RIP) in terms of the chargetransfer interaction in the singlet-triplet energy splitting (J) by taking into account the distance-dependent electronic coupling and reorganization energy. The diffusion-model analysis reveals that the hyperfine-dependent RPM polarization (P _RPM) phase is varied with the driving force (?ΔG _CR) for the charge-recombination (CR) process and that the boundary ?ΔG _CR between the opposite phases coincides well with the total reorganization energy around the diffusible separation distance,r _eff=1.2 nm, between the ion radicals. For the first time, ther _eff is well described by the exponent parameter (β) in the distance-dependent electronic coupling, suggesting that the RPM CIDEP detection can be applied to characterize the electronic coupling in individual solvent-separated RIP systems. It has been concluded that, in contrast to the spin exchange interaction of the neutral radical pairs, the characteristic long-range charge-transfer interaction enables us to utilize the simple diffusion-model analysis to successfully evaluate ther _eff and theP _RPM in homogeneous liquid polar solvents.