TY - JOUR
AU - Angulo, Gonzalo
AU - Jedrak, Jakub
AU - Ochab-Marcinek, Anna
AU - Pasitsuparoad, Pakorn
AU - Radzewicz, Czeslaw
AU - Wnuk, Pawel
AU - Rosspeintner, Arnulf
TI - How good is the generalized Langevin equation to describe the dynamics of photo-induced electron transfer in fluid solution?
PY - 2017
JF - The Journal of Chemical Physics
JA - The J. Chem. Phys.
SN - 0021-9606
VL - 146
IS - 24
SP - 244505
L1 - http://aip.scitation.org/doi/pdf/10.1063/1.4990044
L2 - http://aip.scitation.org/doi/full/10.1063/1.4990044
L3 - http://aip.scitation.org/doi/abs/10.1063/1.4990044
M3 - 10.1063/1.4990044
UR - http://dx.doi.org/10.1063/1.4990044
KW - fluorescence
KW - spectroscopy
KW - chemical reactions
KW - computer simulation
KW - thermodynamic properties
N2 - The dynamics of unimolecular photo-triggered reactions can be strongly affected by the surrounding medium for which a large number of theoretical descriptions have been used in the past. An accurate description of these reactions requires knowing the potential energy surface and the friction felt by the reactants. Most of these theories start from the Langevin equation to derive the dynamics, but there are few examples comparing it with experiments. Here we explore the applicability of a Generalized Langevin Equation (GLE) with an arbitrary potential and a non-Markovian friction. To this end, we have performed broadband fluorescence measurements with sub-picosecond time resolution of a covalently linked organic electron donor-acceptor system in solvents of changing viscosity and dielectric permittivity. In order to establish the free energy surface (FES) of the reaction, we resort to stationary electronic spectroscopy. On the other hand, the dynamics of a non-reacting substance, Coumarin 153, provide the calibrating tool for the non-Markovian friction over the FES, which is assumed to be solute independent. A simpler and computationally faster approach uses the Generalized Smoluchowski Equation (GSE), which can be derived from the GLE for pure harmonic potentials. Both approaches reproduce the measurements in most of the solvents reasonably well. At long times, some differences arise from the errors inherited from the analysis of the stationary solvatochromism and at short times from the excess excitation energy. However, whenever the dynamics become slow, the GSE shows larger deviations than the GLE, the results of which always agree qualitatively with the measured dynamics, regardless of the solvent viscosity or dielectric properties. The method applied here can be used to predict the dynamics of any other reacting system, given the FES parameters and solvent dynamics are provided. Thus no fitting parameters enter the GLE simulations, within the applicability limits found for the model in this work.
ID - 1596
ER -