Solvent relaxation effects on the kinetics of photoinduced electron transfer reactions

Abstract

The three-potential surface problem of electron transfer in solution is analyzed using Zusmantype kinetic equations. The model describes ultrafast formation and recombination of radicalion pairs limited by solvent dielectric relaxation. The problem begins with a donor on an electronic excited state surface. The system evolves with crossing to the radical-ion pair surface (with the possibility of recrossing to the excited donor surface included). Solvent relaxation moves the system to lower energy on the radical-ion pair surface where crossing to the ground state neutral surface occurs (with the possibility of recrossing to the radical-ion surface included). Model calculations of the transient radical-ion pair populations are presented. The time dependent results that are presented show a dramatic dependence on the relative free energy differences (AG 's) among the three potential surfaces. Comparisons to other formalisms and to less detailed approximations are made. The mean populations of the transient species for a system of a donor and many acceptors in the absence of spatial diffusion are also derived.

Hot recombination of photogenerated ion pairs

“…It should be noted that the spatial motion of the reactants was not considered in previous investigations of hot transitions. 5,6,[20][21][22][23] In particular, in Ref. 21 the average lifetime of the immobile ion pairs subjected to hot and thermal recombination was calculated.…”

“…In the following, only the results of the last two papers 22,23 will be used. They will be incorporated in the unified theory ͑UT͒ of irreversible photoionization and recombination, which accounts for the r dependence of all electron transfer rates and the encounter diffusion of the counterions in a Coulomb well.…”

“…Using the most general stochastic approach to the problem, the reversible transfer between three intersecting levels, D * A, D + A − , and DA, has been studied in Ref. 22. The arrangement of the energy levels in the case E of Fig.…”

“…In the case of fast transfer, the kinetics of ion-pair decay consists of a fast hot recombination and a subsequent much slower thermal recombination. 22 Perturbation theory holds only in the opposite limit of the weak transfer where the hot stage is almost eliminated ͓Fig. 4͑b͒ of the same work͔.…”

Influence of spectral characteristics of the pump pulse on the transient absorption of donor–acceptor complexes in polar solvents

“…That is why it could be expected that only one additional parameter, an angle, should appear in the final expression for the signal measured by the pump-probe technique. This angle is not a free parameter and can be determined if the distributions of charges at each transition stage are known [10,[14][15][16][17].…”