A Computational Approach to Modeling Excitation-Energy Transfer and Quenching in Light-Harvesting Complexes

Light-harvesting complexes (LHC) are known to regulate the flux of energy in different light conditions and activate quenching processes to prevent photodamage in case of high light. However, the molecular mechanisms behind these photoprotective processes remain unclear. A widely accepted model suggests an excitation-energy transfer from excited chlorophylls to neighboring carotenoids which finally act as quenchers. Herein, we present a computational protocol to model the energy pathways in the LHC, focusing specifically on the minor CP29 antenna complex of plants. We explore the factors that modulate the switch between light-harvesting and quenched states. The protocol includes modeling the exciton Hamiltonian of the chlorophylls/lutein aggregate, and calculating population dynamics using a kinetic model based on the Redfield-Forster approach. Our analysis reveals a highly tunable excited-state lifetime for the complex, that can switch between quenched and unquenched state depending on the lutein S1 energy, in accordance with recent experiments. Moreover, we observe that the s-trans lutein conformers are more likely to exhibit the characteristics of the quencher.