Structure-Dynamics Relation in Physically-Plausible Multi-Chromophore Systems

Abstract

We study a large number of physically-plausible arrangements of chromophores, generated via a computational method involving stochastic real-space transformations of a naturally occurring 'reference' structure, illustrating our methodology using the well-studied Fenna-Matthews-Olson complex (FMO). To explore the idea that the natural structure has been tuned for efficient energy transport we use an atomic transition charge method to calculate the excitonic couplings of each generated structure and a Lindblad master equation to study the quantum transport of an exciton from a 'source' to a 'drain' chromophore. We find significant correlations between structure and transport efficiency: High-performing structures tend to be more compact and, among those, the best structures display a certain orientation of the chromophores, particularly the chromophore closest to the source-to-drain vector. We conclude that, subject to reasonable, physically-motivated constraints, the FMO complex is highly attuned to the purpose of energy transport, partly by exploiting these structural motifs.The process of excitonic energy transport is of great interest across many fields of study, from evolutionary biology to the engineering of solar cells. It is a key component of both natural photosynthesis (occurring in light harvesting complexes (LHCs), which are assemblages of chromophores found in a famously 'warm and wet' environment) and artificial photovoltaics. It is tempting to suggest that, since natural selection has had perhaps billions of years [1] over which to improve the efficiency of the process, we might learn from nature how to better engineer artificial light harvesting systems. This view has gathered interest in recent years, in tandem with claims that naturally occurring systems can exhibit outstandingly high efficiency [2, 3]. It is often said that quantum coherence could play a pivotal role in enhancing transport [4][5][6][7] through constructive interference of excitation pathways (although this is hotly debated [8][9][10]) and that the structural arrangement of chromophores has been optimised for this functionality [3]. Contrariwise, it might be suggested that efficient transport through a network of chromophores is actually generic and most of the possible structural arrangements would show similar performance. It is difficult to draw conclusions about the general structure-dynamics relationship from studying only a handful of naturally occurring LHCs. Indeed, while it is clearly desirable to learn from the results of natural selection [11], we must also be able to relax the constraints that it operated under in order to uncover the potential for technological advantage, while at all times keeping our imagination on a short enough leash so that any new structures remain physically plausible. * gk@physics.org † animesh.datta@warwick.ac.ukTheoretical efforts have so far proceeded along two paths. The first technique is to randomly 'sprinkle' pointlike electrical dipoles into a restricted volume: This approach has all...

Eliminating radiative losses in long-range exciton transport

“…For simple proof of concept experiments, fine-grained control over energetic gradients, as well as other system parameters, can also be achieved with superconducting circuits [52]. Furthermore, certain natural photosynthetic systems also feature an intrinsic energy gradient [53][54][55][56], and it has been suggested that this may be a key factor in determining transport efficiency [57].…”

Quantum simulation of clustered photosynthetic light harvesting in a superconducting quantum circuit

“…31 In order to obtain the explicit relation between geometry and efficiency, some researches have explored random networks to discover some interesting findings. [32][33][34] Because the EET is sensitively influenced by the interference within the photosynthetic complex, even small changes in the geometry of the complex could turn constructive interference to destructive and thus result in significant drop in the efficiency. Pair sites renders EET properties robust against perturbations.…”

“…32 Compact structures tend to display high performance in the transport dynamics. 33 The networks characterized by Hamiltonians with centrosymmetry outperform those with completely random arrangements. 34 These discoveries seem to suggest that clustered geometries could favor efficient quantum transport.…”

Quantum dissipative systems beyond the standard harmonic model: Features of linear absorption and dynamics

“…The quantum dynamics of a system interacting with an environment is important in many fields of research. Prominent examples of this are found in excitonic energy transport in photosynthesis [1][2][3][4][5][6][7][8][9][10] and the photoisomerisation event of molecular photoswitches [11][12][13] , a key feature in the primary step of vision [14][15][16][17][18][19][20][21] . The presence of the environment, which could be the solution in which a chemical reaction occurs or a protein, introduces the effects of relaxation and dephasing 22 .…”