Quantum modeling of transient infrared spectra reflecting photoinduced electron-transfer dynamics

Abstract

A theoretical description of transient vibrational spectra following the impulsive optical excitation of a molecular system is presented. The approach combines the nonsecular evaluation of the Redfield equations to describe the dissipative dynamics of the system with an efficient implementation of the doorway-window formalism to calculate optical pump/infrared probe (vis/IR) spectra. Both parts of the calculation scale with N2, thus facilitating the treatment of systems with a dimension up to 10(4). The formulation is applied to a simple model of photoinduced electron transfer, which takes into account two coupled electronic states and a single anharmonic vibrational mode. Despite its simplicity, the model is found to exhibit quite complex electronic and vibrational relaxation dynamics, which in turn give rise to rather complex time- and frequency-resolved vis/IR spectra. Interestingly, the calculated IR spectra of the electron-transfer system predict the appearance of novel vibronically induced sidebands, which may even dominate the spectrum at early times.

Nonequilibrium Fermi’s Golden Rule Charge Transfer Rates via the Linearized Semiclassical Method

“…19, we obtain the LSC approximation for C 1 (t′, τ) which is identical to the exact quantum-mechanical result in eq B. 18. Extending to the N-dimensional case, we obtain *E-mail: eitan@umich.edu.…”

“…Extending the analysis to cases where the donor and acceptor PESs have different curvatures, or are anharmonic, , would be highly desirable. Work on such extensions is underway in our group and will be reported separately in future publications.…”

“…Charge transfer (CT) processes in donor–acceptor molecular systems are among the most commonly encountered nonradiative electronic relaxation processes. − They can occur spontaneously, as in redox reactions, or they can be induced by electron injection, as in electrochemical devices, or by photoexcitation, as in photochemical and photovoltaic devices. − …”

Simulation of transient infrared spectra of a photoswitchable peptide

“…(1) by a first-order nonstationary state |ψ t ≡ |ψ(t ) , which is time-dependent due to the initial nonequilibrium preparation of the system. 16,17 Moreover, the IR laser field E(t) is no longer stationary but a laser pulse centered at the delay time t. Assuming, for example, impulsive excitation via a delta function pulse…”

Ultrafast Spectroscopic Signatures of Coherent Electron-Transfer Mechanisms in a Transition Metal Complex

“…31 The model takes inspiration from an earlier nonequilibrium version of Fermi's golden rule in which explicit field−matter interactions were not used to establish the initial condition. 32 Similarly motivated models for nonequilibrium electron transfer 33 and nonsecular transitions between vibrational states 34 have been presented in recent literature. Our model is distinct in that it is specific to an electron-transfer process, the initial condition is determined by explicit field−matter interactions, and multiple promoting modes are treated.…”