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Ultrafast above-threshold dynamics of the radical anion of a prototypical quinone electron-acceptor

Nature Chemistry volume 5, pages 711717 (2013) | Download Citation

Abstract

Quinones feature prominently as electron acceptors in nature. Their electron-transfer reactions are often highly exergonic, for which Marcus theory predicts reduced electron-transfer rates because of a free-energy barrier that occurs in the inverted region. However, the electron-transfer kinetics that involve quinones can appear barrierless. Here, we consider the intrinsic properties of the para-benzoquinone radical anion, which serves as the prototypical electron-transfer reaction product involving a quinone-based acceptor. Using time-resolved photoelectron spectroscopy and ab initio calculations, we show that excitation at 400 and 480 nm yields excited states that are unbound with respect to electron loss. These excited states are shown to decay on a sub-40 fs timescale through a series of conical intersections with lower-lying excited states, ultimately to form the ground anionic state and avoid autodetachment. From an isolated electron-acceptor perspective, this ultrafast stabilization mechanism accounts for the ability of para-benzoquinone to capture and retain electrons.

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Acknowledgements

This work was funded by the Engineering and Physical Sciences Research Council (EP/D073472/1), the Spanish Ministerio de Ciencia e Innovación (MICINN) (CTQ2011-26573 and UNGI08-4E-003 from the European Fund for Regional Development) and the Catalan Agència de Gestió d'Ajuts Universitaris i de Recerca (SGR0528). Q.L. acknowledges a Juan de la Cierva fellowship of the MICINN. J.R.R.V. thanks the European Research Council for a Starting Grant.

Author information

Author notes

    • Daniel A. Horke
    •  & Quansong Li

    Present addresses: Center for Free-Electron Laser Science, DESY, Notkestrasse 85, 22607 Hamburg, Germany (D.A.H.); Key Laboratory of Cluster Science of Ministry of Education, School of Chemistry, Beijing Institute of Technology, 100081 Beijing, China (Q.L.)

Affiliations

  1. Department of Chemistry, University of Durham, Durham DH1 3LE, UK

    • Daniel A. Horke
    •  & Jan R. R. Verlet
  2. Institut de Química Computacional i Catàlisi and Departament de Química, Universitat de Girona, Campus de Montilivi, 17071 Girona, Spain

    • Quansong Li
    •  & Lluís Blancafort

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Contributions

D.A.H. and Q.L. contributed equally to this work. D.A.H. and J.R.R.V. conceived the project and performed all the experiments. Q.L. and L.B. designed and performed all the calculations. Q.L. and D.A.H. analysed the computational and experimental results. All authors discussed the results and contributed to the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Lluís Blancafort or Jan R. R. Verlet.

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DOI

https://doi.org/10.1038/nchem.1705

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