Singlet and triplet energy splitting in the radical ion pairs generated by photoinduced electron-transfer reactions

摘要

Chemically induced dynamic electron polarization (CIDEP) spectra generated by photoinduced electron-transfer reactions have been studied using continuous-wave time- resolved EPR and FTEPR spectroscopy. It has been suggested that the energy difference (#DELTA#E_(ST)) between the singlet and triplet states of radical ion pairs (RIPs) is dependent on the charge recombination free energy (-#DELTA#G_(CR)) and reorganization energy (#gamma#).The result is inter- preted in terms of the spin-selective stabilization or destabilization of RIP states by electron- ic coupling with the So and )ocally excited triplet states of the donor-acceptor pair at equi- librium distance in the .reaction coordinate. It has been .verified that a charge transfer-type exchange interaction governs the .1EST. Magnitudes as well as the sign of #DELTA#E_(ST) can be pre- dicted at the distance of the solvent-separated RIP based on #DELTA#G_(CR) and #gamma# values.