Theoretical-computational modeling of photo-induced charge separation spectra and charge recombination kinetics in solution

Abstract

In this study we propose a theoretical-computational method, essentially based on molecular dynamics simulations and quantum-chemical calculations, for modelling the photo-induced charge separation (CS) and the subsequent charge recombination (CR) processes in solution. In particular we have reproduced the low-energy UV-Vis spectra of systems composed by an aromatic species (Ar = benzene or indene) and tetracyanoethylene (TCNE) in chloroform solution, dominated by the formation of the Ar(+)-TCNE(-) ion pair (IP) complex. The kinetics of the charge recombination process leading to the regeneration of Ar and TCNE has also been modelled. In both the cases the agreement with the experimental data is satisfactory. Although the presence of systematic deficiencies makes our approach unable to address some key aspects of the above processes (e.g. the ultrafast internal vibrational redistribution), it appears to be a rather promising tool for modelling the CS-CR process for atomic-molecular systems of very high complexity. The involvement of the triplet IP complex has also been discussed.

Structural dynamics of an excited donor–acceptor complex from ultrafast polarized infrared spectroscopy, molecular dynamics simulations, and quantum chemical calculations

“…We have chosen to focus on the well-known pair of benzene (Bz, donor) and tetracyanoethylene (TCNE, acceptor) solvated in CH 2 Cl 2 , which has been the subject of recent experimental 36,37 and computational investigations. 38,39 The Bz/TCNE pair has a single CT absorption band peaked near 400 nm, allowing for easy excitation using the doubled fundamental of a Ti:Sapphire laser system, and exhibits sufficiently slow (B50 ps) CR to enable observation of the complete excited state structural dynamics. Additionally, the TCNE radical anion, TCNE À , has strong vibrational markers associated with the CRN stretching modes.…”

Alternative Electron-Transfer Channels Ensure Ultrafast Deactivation of Light-Induced Excited States in Riboflavin Binding Protein

“…By means of a hybrid quantum/classical theoretical–computational approach, similar in spirit to other hybrid methods, ,,− based on MD simulations and the perturbed matrix method (PMM), hereafter termed MD-PMM, we are able to explicitly simulate the kinetics of the ET to the excited Rbf and to provide a detailed picture of the underlying mechanisms. The MD-PMM has been successfully applied for the modeling and calculation of, for example, amide I infrared IR spectra, ultraviolet–visible (UV–vis) absorption spectra, and reduction potentials in proteins. , It has also been applied to model ET reactions in solution − and is here for the first time applied to calculate the ET kinetics inside a protein.…”

“…In the MD-PMM approach, − the part of the system where the quantum processes of interest occur, the quantum center (QC), is treated at the electronic level, and the rest of the system is modeled as an atomic–molecular semiclassical subsystem exerting an electrostatic effect on the QC electronic states. The main difference with the other hybrid methods is that in the MD-PMM the whole system (including the QC) phase space is sampled by classical MD simulations based on typical atomistic empirical/semiempirical force–fields.…”

Theoretical-computational modeling of charge transfer and intersystem crossing reactions in complex chemical systems

“…In fact, by means of proper MD simulations it is rather straightforward to evaluate for a given R and P diabatic states couple the distribution of the time-lengths needed to reach the diabatic energy surfaces crossings in the reactant ensemble of trajectories and thus to reconstruct the [R A ] kinetic trace with the corresponding rate constant (K R A ), as we obtained in previous papers. 53,[56][57][58] Moreover, from the ensemble of the diabatic surfaces crossings as provided by the reactive trajectories it is also possible to obtain a ¼ hc l i by simply evaluating by means of the Landau-Zener approach the adiabatic fraction at each crossing and then averaging over the crossings.…”

“…In this respect MD-PMM, should be perceived as somewhat complementary to the already cited procedures designed for non-BO processes as relies in the extended phase-space sampling of the whole system, allowing the modeling of atomic-molecular systems whose complexity, far beyond the limitations of explicit quantum-dynamical approaches, is an essential and indispensable ingredient for the reliability of the nal result. All the applications carried out so far [56][57][58] have been characterized by two common features. Firstly, all the investigated processes have been limited to Electron Transfer (ET) reactions, i.e.…”