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Volume 221, 2020
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Limits of exciton delocalization in molecular aggregates

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Abstract

Exciton states of molecular aggregates, with a particular focus on delocalization length, are discussed. Despite the huge number of studies of molecular excitons, it is argued that there remain interesting open questions. It is hypothesized that limits for equilibrium delocalization length are generally in the range of tens of molecules, even at very low temperatures. Effects that limit delocalization include: phase disorder from wave-zone electronic coupling, polarization fluctuations, and the extreme sensitivity of perfect delocalization to disorder as the size of the molecular aggregate increases. To gain physical insight, the inverse participation ratio is compared to the order parameter for a classical system of coupled, and hence entrained, oscillators—the Kuramoto model. The main result of the paper is that the inverse participation ratio obtained from the quantum mechanical exciton model and the Kuramoto order parameter obtained from coupled classical oscillators estimate the same coherence length. Conclusions suggest discussion topics that touch on limits of delocalization, quantum-to-classical transitions in molecular exciton systems, and whether excitons are good prospects for exploring and exploiting quantum information resources from coherence.

Graphical abstract: Limits of exciton delocalization in molecular aggregates

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Publication details

The article was received on 09 May 2019, accepted on 11 Jun 2019 and first published on 12 Aug 2019


Article type: Paper
DOI: 10.1039/C9FD00064J
Faraday Discuss., 2020,221, 265-280
  • Open access: Creative Commons BY-NC license
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    Limits of exciton delocalization in molecular aggregates

    G. D. Scholes, Faraday Discuss., 2020, 221, 265
    DOI: 10.1039/C9FD00064J

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