Environmental Effects in the FMO and PE545 Photosynthetic Complexes

Abstract

In most natural photosynthetic systems, light energy is absorbed by antenna pigment-protein complexes and subsequently transferred to a reaction center for conversion to a more stable form. Recent experimental findings in some light-harvesting complexes suggest the existence of long-lived quantum coherences between the individual pigments. A combination of molecular dynamics, quantum chemistry and dynamics can be employed to theoretically contribute to the questions of environmental coupling, spatial correlations between the chromophores, and two-dimensional spectra.Long-lived quantum coherences were observed in the Fenna-Matthews-Olson (FMO) light-harvesting complex as well as in the PE545 complex and have steered considerable effort to explain these findings. Along molecular dynamics trajectories, electronic structure calculations for the vertical excitation energies of the individual bacteriochlorophylls have been performed for different light-harvesting complexes. In addition, the electronic couplings between the pigments have been determined in a time-dependent manner as well. In a first step, the distribution of energies and couplings have been analyzed together with possible spatial correlations. In subsequent steps, ensemble-averaged wave packet dynamics are used to determine the exciton dynamics in the system. Finally, the time-dependent Hamiltonian is used to determine linear and two-dimensional spectra. This allows a direct comparison with experiment. In conclusion, atomistic simulations can be employed to directly determine spectroscopic properties of photosynthetic complexes and help unravel their structure-function relationship including their exciton transfer properties [1-4].[1] M. Aghtar, J. Strumpfer, C. Olbrich, K. Schulten, U. Kleinekathofer, J. Phys. Chem. B 117, 7157 (2013).[2] C. Olbrich, ..., U. Kleinekathofer, J. Phys. Chem. B 115, 8609 (2011).[3] C. Olbrich, J. Strumpfer, K. Schulten, U. Kleinekathofer, J. Phys. Chem. Lett. 2, 1771 (2011).[4] C. Olbrich, J. Strumpfer, K. Schulten, U. Kleinekathofer, J. Phys. Chem. B 115, 758 (2011).