Memory-assisted exciton diffusion in the chlorosome light-harvesting antenna of green sulfur bacteria

TL;DR

This study reveals how memory effects in dynamical disorder facilitate rapid and anisotropic exciton diffusion in chlorosomes, crucial for efficient light-harvesting in green sulfur bacteria.

Contribution

It uncovers the microscopic role of memory effects in exciton delocalization and diffusion within chlorosomes, supported by atomistic simulations and structural data.

Findings

Exciton delocalizes over the entire aggregate in about 200 fs.

Memory effects double the exciton diffusion coefficients.

Diffusion is highly anisotropic, favoring transfer towards the baseplate.

Abstract

Chlorosomes are likely the largest and most efficient natural light-harvesting photosynthetic antenna systems. They are composed of large numbers of bacteriochlorophylls organized into supramolecular aggregates. We explore the microscopic origin of the fast excitation energy transfer in the chlorosome using the recently-resolved structure and atomistic-detail simulations. Despite the dynamical disorder effects on the electronic transitions of the bacteriochlorophylls, our simulations show that the exciton delocalizes over the entire aggregate in about 200 fs. The memory effects associated to the dynamical disorder assist the exciton diffusion through the aggregates and enhance the diffusion coefficients as a factor of two as compared to the model without memory. Furthermore, exciton diffusion in the chlorosome is found to be highly anisotropic with the preferential transfer towards the baseplate, which is the next functional element in the photosynthetic system.