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

Bull, J.N.; West, C.W.; Verlet, J.R.R.

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.

Citation

Bull, J., West, C., & Verlet, J. (2016). Ultrafast dynamics of formation and autodetachment of a dipole-bound state in an open-shell π-stacked dimer anion. Chemical Science, 7(8), 5352-5361. https://doi.org/10.1039/c6sc01062h

• Journal Article Type: Article
• Acceptance Date: Apr 23, 2016
• Online Publication Date: May 4, 2016
• Publication Date: Aug 1, 2016
• Deposit Date: Jun 14, 2016
• Publicly Available Date: Jun 14, 2016
• Journal: Chemical Science
• Print ISSN: 2041-6520
• Electronic ISSN: 2041-6539
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 7
• Issue: 8
• Pages: 5352-5361
• DOI: https://doi.org/10.1039/c6sc01062h
• Public URL: https://durham-repository.worktribe.com/output/1381000