Optically Induced Electron Transfer in Mixed-Valence States: A Model Study on Electronic Transitions, Relaxation Dynamics, and Transient Absorption Spectroscopy

Abstract

Quantum dynamical model calculations are performed on the optically induced electron transfer in a mixed-valence system interacting with different solvents. The simultaneously occurring processes of population transfer between electronic states and relaxation are studied in detail. Transient absorption traces, as recently recorded in our laboratory, are simulated, and the features of the spectra are related to the dynamics. The agreement with the experiment hints at the fact that the employed one-dimensional models catch the essentials of the photochemistry of the investigated systems and that they can be used for the interpretation of the transient absorption spectra. It is inferred that the ultrafast electron transfer processes take place on a sub-picosecond time scale and afterward relaxation occurs within several picoseconds.

Optically Induced Charge Transfer in Organic Mixed-Valence Systems: Wave Packet Dynamics and Femtosecond Transient Spectroscopy

“…For the system 3 + the time-delayed probe pulse has a photon energy of 0.6 eV, a fwhm of 1.0 eV, and a temporal half-width of 3.6 fs. This short pulse duration is used in order to approximate a white-light continuum as employed in our former transient-absorption experiments on mixed-valence compounds. , The coupling strengths are A 2 μ 12 = 0.085 eV and A 2 μ 23 = 0.199 eV. Transient absorption spectra, taken at selected times are shown in Figure , lower panel.…”

“…To incorporate the interaction of the system with a bath, we use the quantum-jump method. , The algorithm adapted to models like the one used in this work has been described before, and we only briefly summarize the basic propagation steps in what follows. First, the field-free propagation is discussed.…”

“…In a former quantum dynamical study, we employed a one-dimensional approach to study the laser-induced hole transfer in a symmetrically bridged MV compound . Despite the simplicity of the model, it was possible to reproduce transient absorption spectra taken in different solvents .…”

“…35,36 In a former quantum dynamical study, we employed a onedimensional approach to study the laser-induced hole transfer in a symmetrically bridged MV compound. 37 Despite the simplicity of the model, it was possible to reproduce transient absorption spectra taken in different solvents. 38 The calculations that incorporated coupled educt and product potentials, obviously suffer from the neglect of bridge localized states, and thus the role of the latter in the transfer process remained unclear.…”

Equation-of-Motion Methods for the Calculation of Femtosecond Time-Resolved 4-Wave-Mixing and N-Wave-Mixing Signals

“…The norm is restored by randomly occurring quantum jumps according to a certain jump probability. A variant of the quantum jump SSE by Makarov and Metiu has been combined with perturbation theory with respect to the laser pulses, providing an efficient method for the simulation of third-order and fifth-order − 2D spectra. The approach was employed within the EOM framework to evaluate TA PP responses induced by a strong pump pulse .…”