Quantum redirection of antenna absorption to photosynthetic reaction centres

TL;DR

This paper demonstrates how excitonic delocalisation enhances the absorption of reaction centres in photosynthesis and shows how this phenomenon can be harnessed to direct excitations in artificial nanostructures.

Contribution

It reveals the role of excitonic delocalisation in redistributing dipole strengths and guiding excitations towards reaction centres, with implications for artificial photosynthetic systems.

Findings

Excitonic delocalisation increases RC absorption cross section.

Redistribution is robust to microscopic dephasing details.

Coherent dynamics can be directed in artificial structures.

Abstract

The early steps of photosynthesis involve the photo-excitation of reaction centres (RCs) and light-harvesting (LH) units. Here, we show that the --historically overlooked-- excitonic delocalisation across RC and LH pigments results in a redistribution of dipole strengths that benefits the absorption cross section of the optical bands associated with the RC of several species. While we prove that this redistribution is robust to the microscopic details of the dephasing between these units in the purple bacterium Rhodospirillum rubrum, we are able to show that the redistribution witnesses a more fragile, but persistent, coherent population dynamics which directs excitations from the LH towards the RC units under incoherent illumination and physiological conditions. Stochastic optimisation allows us to delineate clear guidelines and develop simple analytic expressions, in order to achieve directed coherent population dynamics in artificial nano-structures.