Atomistic study of energy funneling in the light-harvesting complex of green sulfur bacteria

TL;DR

This study introduces an atomistic model of green sulfur bacteria's light-harvesting complex, revealing how energy funneling occurs efficiently and robustly through multiple channels and mechanisms, explaining experimental observations.

Contribution

The paper presents a detailed atomistic model of the entire light-harvesting system, elucidating the physical mechanisms behind efficient energy transfer in green sulfur bacteria.

Findings

Energy funneling results from fast intra-subunit relaxation and inter-subunit transfer.

Energy transfer is robust against initial conditions and temperature variations.

Multiple energy transport channels operate across different length scales.

Abstract

Phototrophic organisms such as plants, photosynthetic bacteria and algae use microscopic complexes of pigment molecules to absorb sunlight. Within the light-harvesting complexes, which frequently have several functional and structural subunits, the energy is transferred in the form of molecular excitations with very high efficiency. Green sulfur bacteria are considered to be amongst the most efficient light-harvesting organisms. Despite multiple experimental and theoretical studies of these bacteria the physical origin of the efficient and robust energy transfer in their light-harvesting complexes is not well understood. To study excitation dynamics at the systems level we introduce an atomistic model that mimics a complete light-harvesting apparatus of green sulfur bacteria. The model contains approximately 4000 pigment molecules and comprises a double wall roll for the chlorosome, a baseplate and six Fenna-Matthews-Olson trimer complexes. We show that the fast relaxation within functional subunits combined with the transfer between collective excited states of pigments can result in robust energy funneling. Energy transfer is robust on the initial excitation conditions and temperature changes. Moreover, the same mechanism describes the coexistence of multiple timescales of excitation dynamics frequently observed in ultrafast optical experiments. While our findings support the hypothesis of supertransfer, the model reveals energy transport through multiple channels on different length scales.