(710b) Modeling Biomolecular Structure and Excitation Energy Transfer in Photosynthetic Pigment-Protein Complexes

In photosynthetic organisms, the mechanisms by which photosynthetic pigment-protein complexes transfer harvested energy efficiently to their photosystems must be better understood at the molecular scale, so that these mechanisms can be applied to building inexpensive and efficient bio-hybrid photovoltaics.  Using the peridinin-chlorophyll a-protein (PCP) from marine algae as a model photosynthetic light-harvesting complex (LHC), we model excitation energy transfer in the complex using both a Förster resonance energy transfer (FRET) model and a semi-classical propagation scheme.  To model the rates and efficiencies of excitation energy transfer in PCP using FRET, we first calculate absorption/fluorescence spectra and transition dipole moments from the electronic excited states using time-dependent density functional theory (TD-DFT). We use a QM/MM approach to determine the biomolecular structure of PCP and the effect of the protein scaffold on the rates and efficiencies of excitation energy transfer.  We also present our development of a semi-classical propagation scheme to observe the dynamical evolution of the excited state wavefunctions, by constructing an initial model Hamiltonian of the PCP complex and calculating the time correlation of the wavefunctions.  Both models are compared to experimental spectroscopic measurements, and implications for quantum coherence in bio-hybrid photovoltaics are discussed.