Optical signatures of quantum delocalization over extended domains in photosynthetic membranes

TL;DR

This paper theoretically demonstrates that optical absorption spectra can reveal excitonic delocalization and coherent coupling in photosynthetic membranes, aiding understanding of energy transfer mechanisms.

Contribution

It introduces a method to detect excitonic delocalization in extended light-harvesting complexes via optical signatures in absorption spectra.

Findings

Optical spectra show signatures of excitonic delocalization.

Polarized and unpolarized absorption can diagnose coherent coupling.

Method helps estimate F"orster transfer rates.

Abstract

The prospect of coherent dynamics and excitonic delocalization across several light-harvesting structures in photosynthetic membranes is of considerable interest, but challenging to explore experimentally. Here we demonstrate theoretically that the excitonic delocalization across extended domains involving several light-harvesting complexes can lead to unambiguous signatures in the optical response, specifically, linear absorption spectra. We characterize, under experimentally established conditions of molecular assembly and protein-induced inhomogeneities, the optical absorption in these arrays from polarized and unpolarized excitation, and demonstrate that it can be used as a diagnostic tool to determine the coherent coupling among iso-energetic light-harvesting structures. The knowledge of these couplings would then provide further insight into the dynamical properties of transfer, such as facilitating the accurate determination of F\"orster rates.