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Issue 8, 2016
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Ultrafast dynamics of formation and autodetachment of a dipole-bound state in an open-shell π-stacked dimer anion

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Abstract

Isolated π-stacked dimer radical anions present the simplest model of an excess electron in a π-stacked environment. Here, frequency-, angle-, and time-resolved photoelectron imaging together with electronic structure calculations have been used to characterise the π-stacked coenzyme Q0 dimer radical anion and its exited state dynamics. In the ground electronic state, the excess electron is localised on one monomer with a planar para-quinone ring, which is solvated by the second monomer in which carbonyl groups are bent out of the para-quinone ring plane. Through the π-stacking interaction, the dimer anion exhibits a number of charge-transfer (intermolecular) valence-localised resonances situated in the detachment continuum that undergo efficient internal conversion to a cluster dipole-bound state (DBS) on a ∼60 fs timescale. In turn, the DBS undergoes vibration-mediated autodetachment on a 2.0 ± 0.2 ps timescale. Experimental vibrational structure and supporting calculations assign the intermolecular dynamics to be facilitated by vibrational wagging modes of the carbonyl groups on the non-planar monomer. At photon energies ∼0.6–1.0 eV above the detachment threshold, a competition between photoexcitation of an intermolecular resonance leading to the DBS, and photoexcitation of an intramolecular resonance leading to monomer-like dynamics further illustrates the π-stacking specific dynamics. Overall, this study provides the first direct observation of both internal conversion of resonances into a DBS, and characterisation of a vibration-mediated autodetachment in real-time.

Graphical abstract: Ultrafast dynamics of formation and autodetachment of a dipole-bound state in an open-shell π-stacked dimer anion

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Publication details

The article was received on 07 Mar 2016, accepted on 23 Apr 2016 and first published on 04 May 2016


Article type: Edge Article
DOI: 10.1039/C6SC01062H
Citation: Chem. Sci., 2016,7, 5352-5361
  • Open access: Creative Commons BY license
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    Ultrafast dynamics of formation and autodetachment of a dipole-bound state in an open-shell π-stacked dimer anion

    J. N. Bull, C. W. West and J. R. R. Verlet, Chem. Sci., 2016, 7, 5352
    DOI: 10.1039/C6SC01062H

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