Transient Spectral Features of a cis−trans Photoreaction in the Condensed Phase:  A Model Study

Abstract

A theoretical description to calculate transient absorption spectra of photoreactive systems in the condensed phase is developed. The formulation comprises a multidimensional model of nonadiabatic photoisomerization, a Redfield treatment of the environment within the secular approximation, and a doorway−window formulation to calculate transient pump−probe spectra. Employing the eigenstate representation and assuming Gaussian laser pulses, we derive explicit expressions for the doorway and window operators. The formalism scales with N 2 (N being the dimension of the system Hamiltonian matrix) and therefore allows us to handle multidimensional molecular models. Detailed computational studies of the dynamics and transient absorption are presented for various cis−trans photoisomerization models. It is shown that only the two-mode model involving a conical intersection yields short-time transients, as expected for a condensed-phase system. Problems in the interpretation of transient spectra associated with the competition (and cancellation) of the various spectroscopic contributions in a photoreaction are discussed in some detail. The computational studies demonstrate the need for theoretical modeling in order to achieve a microscopic interpretation of femtosecond experiments.

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

“…The approach combines the nonsecular evaluation 28 of the Redfield equation to describe the dissipative dynamics of the system with an efficient implementation of the doorway-window formalism 33 to calculate timeand frequency-resolved vis/IR spectra. The approach combines the nonsecular evaluation 28 of the Redfield equation to describe the dissipative dynamics of the system with an efficient implementation of the doorway-window formalism 33 to calculate timeand frequency-resolved vis/IR spectra.…”

Dissipative dynamics at conical intersections: simulations with the hierarchy equations of motion method

“…Early studies of the effects of an external bath on the photoinduced dynamics of two-mode and three-mode conical intersections were performed by Gerdts and Manthe, 18 Kühl and Domcke 19,20 and Baltzer and Stock, 21,22 assuming bilinear coupling of the active modes of the conical intersection to a harmonic bath with ohmic spectral density. The dissipative dynamics of these systems was numerically simulated with multi-level Redeld theory 23,24 which is valid within the limits of weak system-bath coupling and short memory relaxation time of the bath.…”

Relaxation dynamics through a conical intersection: Quantum and quantum–classical studies

“…Electronic ground (S 0 ) and first-excited (S 1 ) singlet states present a conical intersection at some geometry, as will be shown in the following. The reduced dimensionality of the model, and the fact that it is parametrized to reproduce features observed in Raman and time-resolved experiments 38 , made it for long time the preferred choice to study the ultrafast relaxation process of the photo-excited retinal based on quantum-dynamical simulations 11,[40][41][42][43][44][45][46][47][48][49][50][51] . To our knowledge, however, trajectory-based methods have not yet been employed, systematically, in combination with this model 44,49,52 .…”