Photoinduced electron transfer in mixed-valence compounds: Beyond the golden rule regime

Abstract

The short-time charge transfer evolution following photoexcitation in mixed valence compounds is studied using path integral calculations. Due to the large nonadiabatic coupling, path integral calculations using direct path summation techniques are inadequate, and charge transfer dynamics can only be computed using a transfer matrix technique developed by Makri and Makarov. The resulting relaxation is considerably slower than that predicted by low-order perturbation theory. The effects of the solvent on the decay process, and the validity of the golden rule to predict the dynamics of the decay process are investigated. The effects of preparing an initial state that is not a rovibrational state of the acceptor potential energy surface is also examined. These exact calculations show that the large electronic mixing gives rise to very fast oscillations in the electronic state population as the wave function oscillates coherently between the donor and acceptor. This is followed by a slower relaxation induced by the coupling to the dissipative solvent modes, which occurs on time scales ⩽100 fs. This information provides insight into the mechanism for oscillations observed in time-resolved transient spectra of these compounds, and suggests substantial limitations of the golden rule picture.

Solvent Effects in Nonadiabatic Electron‐Transfer Reactions: Theoretical Aspects

“…Exact enumeration method (dashed) and the transfer matrix path integral approach (solid) are compared with the Golden Rule prediction (dash-dotted). (Reproduced from [132] with permission. Copyright (1998) by the American Institute of Physics.)…”

“…Mak and Egger [124f,h] also recently suggested a very promising procedure to resolve the dynamical sign problem -the so-called multilevel blocking approach. For the description of the short time evolution (tV : 10) it is possible to use direct summation of all the paths [132]. ( * in our notation) obtained via real time path integral QMC calculations for nonadiabatic transitions between harmonic diabatic states with frequency : 500 cm\ and electronic coupling V : 0.1 in the presence of Ohmic dissipation with exponential cutoff at .…”

Semiclassical treatments of electron transfer rate from weak to strong electronic coupling regime

“…Note that the alternative studies [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] based on the multidimensional dynamical approaches have also been carried out on considering the electronic population relaxation and its transient non-equilibrium properties. These approaches are useful for the dynamical investigation, but when the intramolecular modes are explicitly incorporated their numerical convergence for the rate calculation is still a dilemma [39].…”

Coherent and incoherent photon-assisted electron tunneling in optoelectronic molecular devices in soft solids

“…For example, the use of molecules for these purposes would allow for high component density, increased response speeds, and very high energy efficiency. Because of their small size, there have been many discussions regarding the possibility of increasing data-storage density to as much as 10 18 bits per square centimeter with the use in molecular switchers. 2 Also, since electron transfer occurs within the molecules on picosecond or even femtosecond time scale, it should be possible to produce devices that respond extremely rapidly.…”