Optimal Efficiency of Self-Assembling Light-Harvesting Arrays

TL;DR

This paper investigates how network structure, transfer rates, and component ratios influence energy transfer efficiency in self-assembling light-harvesting arrays, providing analytical and simulation insights for optimal design.

Contribution

It offers analytical expressions and design principles for optimizing energy transfer efficiency in complex chromophore networks, including higher-dimensional and self-assembling structures.

Findings

Efficiency increases steeply with D-to-A transfer rate when decay is slow.

Introducing B chromophores can improve efficiency in certain systems.

Staggered conformations are more efficient than eclipsed in stacked-disk models.

Abstract

Using a classical master equation that describes energy transfer over a given lattice, we explore how energy transfer efficiency along with the photon capturing ability depends on network connectivity, on transfer rates, and on volume fractions - the numbers and relative ratio of fluorescence chromophore components, e.g., donor (D), acceptor (A), and bridge (B) chromophores. For a one-dimensional AD array, the exact analytical expression for efficiency shows a steep increase with a D-to-A transfer rate when a spontaneous decay is sufficiently slow. This result implies that the introduction of B chromophores can be a useful method for improving efficiency for a two-component AD system with inefficient D-to-A transfer and slow spontaneous decay. Analysis of this one-dimensional system can be extended to higher-dimensional systems with chromophores arranged in structures such as a helical or stacked-disk rod, which models the self-assembling monomers of the tobacco mosaic virus coat protein. For the stacked-disk rod, we observe the following: (1) With spacings between sites fixed, a staggered conformation is more efficient than an eclipsed conformation. (2) For a given ratio of A and D chromophores, the uniform distribution of acceptors that minimizes the mean first passage time to acceptors is a key point to designing the optimal network for a donor-acceptor system with a relatively small D-to-A transfer rate. (3) For a three-component ABD system with a large B-to-A transfer rate, a key design strategy is to increase the number of the pathways in accordance with the directional energy flow from D to B to A chromophores.