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Design Principles for Long-Range Energy Transfer at Room Temperature

Andrea Mattioni, Felipe Caycedo-Soler, Susana F. Huelga, and Martin B. Plenio
Phys. Rev. X 11, 041003 – Published 6 October 2021
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Abstract

Under physiological conditions, ballistic long-range transfer of electronic excitations in molecular aggregates is generally expected to be suppressed by noise and dissipative processes. Hence, quantum phenomena are not considered to be relevant for the design of efficient and controllable energy transfer over significant length scales and timescales. Contrary to this conventional wisdom, here we show that the robust quantum properties of small configurations of repeating clusters of molecules can be used to tune energy-transfer mechanisms that take place on much larger scales. With the support of an exactly solvable model, we demonstrate that coherent exciton delocalization and dark states within unit cells can be used to harness dissipative phenomena of varying nature (thermalization, fluorescence, nonradiative decay, and weak intersite correlations) to support classical propagation over macroscopic distances. In particular, we argue that coherent delocalization of electronic excitations over just a few pigments can drastically alter the relevant dissipation pathways that influence the energy-transfer mechanism and thus serve as a molecular control tool for large-scale properties of molecular materials. Building on these principles, we use extensive numerical simulations to demonstrate that they can explain currently not-understood measurements of micron-scale exciton diffusion in nanofabricated arrays of bacterial photosynthetic complexes. Based on these results, we provide quantum design guidelines at the molecular scale to optimize both energy-transfer speed and range over macroscopic distances in artificial light-harvesting architectures.

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  • Received 4 June 2019
  • Revised 15 July 2021
  • Accepted 19 July 2021

DOI:https://doi.org/10.1103/PhysRevX.11.041003

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied PhysicsInterdisciplinary Physics

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Rising Above the Quantum Noise

Published 6 October 2021

The control of molecular-level quantum effects in artificial photosynthetic membranes is a powerful tuning knob for optimizing long-range energy transport, according to a theoretical study.

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Authors & Affiliations

Andrea Mattioni, Felipe Caycedo-Soler*, Susana F. Huelga, and Martin B. Plenio

  • Institut für Theoretische Physik and Center for Integrated Quantum Science and Technology IQST, Albert-Einstein-Allee 11, Universität Ulm, 89069 Ulm, Germany

  • *Deceased.
  • martin.plenio@uni-ulm.de
  • Present address: Department of Chemistry, School of Natural Sciences, The University of Manchester, Oxford Road, Manchester, M13 9PL, United Kingdom.

Popular Summary

In general, the more efficiently a molecule absorbs light, the more strongly it will fluoresce. While crucial for some applications, this feature is highly detrimental for tasks relying on efficient transport and storage of harvested solar energy, such as photosynthesis or photovoltaics, limiting the distance across which energy can be transported. Based on theoretical analysis and extensive numerical simulations of natural light-harvesting molecules, we show how robust quantum interference can be harnessed microscopically to overcome this limitation, allowing energy to flow for much greater distances than previously thought possible before being dissipated as photons.

We consider a model system composed of strongly coupled pigments arranged in modular units. Quantum dynamics leads to the formation of coherently delocalized electronic excited states within these units. Some of these units effectively decouple from optical fields and become “dark,” thereby protecting their excitations from fluorescence. This decoupling also slows down their energy-transfer dynamics under typical physiological conditions. By solving the model analytically, we demonstrate that close packing of light-harvesting units promotes the activation of local dark states, which can increase the exciton diffusion length by several orders of magnitude, albeit while slowing down energy transfer.

Crucially, this model determines design principles based on delocalization within modular unit cells for efficient excitation energy transport on macroscopic length scales in realistic scenarios. We show how these concepts apply to biological structures by explaining experimental results that have escaped a comprehensive theoretical framework until now.

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Vol. 11, Iss. 4 — October - December 2021

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