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  • 1. Eckert, Sebastian
    et al.
    Norell, Jesper
    Stockholm University, Faculty of Science, Department of Physics.
    Jay, Raphael M.
    Fondell, Mattis
    Mitzner, Rolf
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Föhlisch, Alexander
    T-1 Population as the Driver of Excited-State Proton-Transfer in 2-Thiopyridone2019In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 25, no 7, p. 1733-1739Article in journal (Refereed)
    Abstract [en]

    Excited-state proton transfer (ESPT) is a fundamental process in biomolecular photochemistry, but its underlying mediators often evade direct observation. We identify a distinct pathway for ESPT in aqueous 2-thiopyridone, by employing transient N1s X-ray absorption spectroscopy and multi-configurational spectrum simulations. Photoexcitations to the singlet S-2 and S-4 states both relax promptly through intersystem crossing to the triplet T-1 state. The T-1 state, through its rapid population and near nanosecond lifetime, mediates nitrogen site deprotonation by ESPT in a secondary intersystem crossing to the S-0 potential energy surface. This conclusively establishes a dominant ESPT pathway for the system in aqueous solution, which is also compatible with previous measurements in acetonitrile. Thereby, the hitherto open questions of the pathway for ESPT in the compound, including its possible dependence on excitation wavelength and choice of solvent, are resolved.

  • 2. Eckert, Sebastian
    et al.
    Norell, Jesper
    Stockholm University, Faculty of Science, Department of Physics.
    Miedema, Piter S.
    Beye, Martin
    Fondell, Mattis
    Quevedo, Wilson
    Kennedy, Brian
    Hantschmann, Markus
    Pietzsch, Annette
    Van Kuiken, Benjamin E.
    Ross, Matthew
    Minitti, Michael P.
    Moeller, Stefan P.
    Schlotter, William F.
    Khalil, Munira
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Föhlisch, Alexander
    Ultrafast Independent N-H and N-C Bond Deformation Investigated with Resonant Inelastic X-Ray Scattering2017In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 56, no 22, p. 6088-6092Article in journal (Refereed)
    Abstract [en]

    The femtosecond excited-state dynamics following resonant photoexcitation enable the selective deformation of N-H and N-C chemical bonds in 2-thiopyridone in aqueous solution with optical or X-ray pulses. In combination with multiconfigurational quantum-chemical calculations, the orbital-specific electronic structure and its ultrafast dynamics accessed with resonant inelastic X-ray scattering at the N 1s level using synchrotron radiation and the soft X-ray free-electron laser LCLS provide direct evidence for this controlled photoinduced molecular deformation and its ultrashort time-scale.

  • 3. Jay, Raphael M.
    et al.
    Eckert, Sebastian
    Fondell, Mattis
    Miedema, Piter S.
    Norell, Jesper
    Stockholm University, Faculty of Science, Department of Physics.
    Pietzsch, Annette
    Quevedo, Wilson
    Niskanen, Johannes
    Kunnus, Kristjan
    Föhlisch, Alexander
    The nature of frontier orbitals under systematic ligand exchange in (pseudo-)octahedral Fe(II) complexes2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 44, p. 27745-27751Article in journal (Refereed)
    Abstract [en]

    Understanding and controlling properties of transition metal complexes is a crucial step towards tailoring materials for sustainable energy applications. In a systematic approach, we use resonant inelastic X-ray scattering to study the influence of ligand substitution on the valence electronic structure around an aqueous iron(II) center. Exchanging cyanide with 2-2'-bipyridine ligands reshapes frontier orbitals in a way that reduces metal 3d charge delocalization onto the ligands. This net decrease of metal-ligand covalency results in lower metal-centered excited state energies in agreement with previously reported excited state dynamics. Furthermore, traces of solvent-effects were found indicating a varying interaction strength of the solvent with ligands of different character. Our results demonstrate how ligand exchange can be exploited to shape frontier orbitals of transition metal complexes in solution-phase chemistry; insights upon which future efforts can built when tailoring the functionality of photoactive systems for light-harvesting applications.

  • 4. Jay, Raphael M.
    et al.
    Norell, Jesper
    Stockholm University, Faculty of Science, Department of Physics.
    Eckert, Sebastian
    Hantschmann, Markus
    Beye, Martin
    Kennedy, Brian
    Quevedo, Wilson
    Schlotter, William F.
    Dakovski, Georgi L.
    Minitti, Michael P.
    Hoffmann, Matthias C.
    Mitra, Ankush
    Moeller, Stefan P.
    Nordlund, Dennis
    Zhang, Wenkai
    Liang, Huiyang W.
    Kunnus, Kristian
    Kubicek, Katharina
    Techert, Simone A.
    Lundberg, Marcus
    Wernet, Philippe
    Gaffney, Kelly
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Föhlisch, Alexander
    Disentangling Transient Charge Density and Metal-Ligand Covalency in Photoexcited Ferricyanide with Femtosecond Resonant Inelastic Soft X-ray Scattering2018In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 9, no 12, p. 3538-3543Article in journal (Refereed)
    Abstract [en]

    Soft X-ray spectroscopies are ideal probes of the local valence electronic structure of photocatalytically active metal sites. Here, we apply the selectivity of time resolved resonant inelastic X-ray scattering at the iron L-edge to the transient charge distribution of an optically excited charge-transfer state in aqueous ferricyanide. Through comparison to steady-state spectra and quantum chemical calculations, the coupled effects of valence-shell closing and ligand-hole creation are experimentally and theoretically disentangled and described in terms of orbital occupancy, metal-ligand covalency, and ligand field splitting, thereby extending established steady-state concepts to the excited-state domain. pi-Back-donation is found to be mainly determined by the metal site occupation, whereas the ligand hole instead influences sigma-donation. Our results demonstrate how ultrafast resonant inelastic X-ray scattering can help characterize local charge distributions around catalytic metal centers in short-lived charge-transfer excited states, as a step toward future rationalization and tailoring of photocatalytic capabilities of transition-metal complexes.

  • 5.
    Norell, Jesper
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Fasolino, Annalisa
    de Wijn, Astrid S.
    Stockholm University, Faculty of Science, Department of Physics. Norwegian University of Science and Technology, Norway.
    Emergent friction in two-dimensional Frenkel-Kontorova models2016In: Physical Review E, ISSN 2470-0045, Vol. 94, no 2, article id 023001Article in journal (Refereed)
    Abstract [en]

    Simple models for friction are typically one-dimensional, but real interfaces are two-dimensional. We investigate the effects of the second dimension on static and dynamic friction by using the Frenkel-Kontorova (FK) model. We study the two most straightforward extensions of the FK model to two dimensions and simulate both the static and dynamic properties. We show that the behavior of the static friction is robust and remains similar in two dimensions for physically reasonable parameter values. The dynamic friction, however, is strongly influenced by the second dimension and the accompanying additional dynamics and parameters introduced into the models. We discuss our results in terms of the thermal equilibration and phonon dispersion relations of the lattices, establishing a physically realistic and suitable two-dimensional extension of the FK model. We find that the presence of additional dissipation channels can increase the friction and produces significantly different temperature dependence when compared to the one-dimensional case. We also briefly study the anisotropy of the dynamic friction and show highly nontrivial effects, including that the friction anisotropy can lead to motion in different directions depending on the value of the initial velocity.

  • 6.
    Norell, Jesper
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Grell, Gilbert
    Kühn, Oliver
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Bokarev, Sergey I.
    Photoelectron shake-ups as a probe of molecular symmetry: 4d XPS analysis of I-3(-) in solution2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 30, p. 19916-19921Article in journal (Refereed)
    Abstract [en]

    A combination of multi-configurational restricted active space calculations with a Dyson orbital formalism has been applied for accurate simulations of 4d photo-electron spectra of the I-3(-) molecular ion. The analysis based on the occupation numbers of natural orbitals allowed to predict and rationalize the spectral fingerprints of solvent-induced nuclear asymmetry. In particular, it demonstrates how the nuclear asymmetry directly causes an increase of shake-up intensity. The relative intensity of shake-up and main features of the I 4d XPS spectrum could therefore serve as a simplified experimental observable of structural asymmetry, complementary to changes in the shape of the main spectral features.

  • 7.
    Norell, Jesper
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Jay, Raphael M.
    Hantschmann, Markus
    Eckert, Sebastian
    Guo, Meiyuan
    Gaffney, Kelly J.
    Wernet, Philippe
    Lundberg, Marcus
    Föhlisch, Alexander
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Fingerprints of electronic, spin and structural dynamics from resonant inelastic soft X-ray scattering in transient photo-chemical species2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 10, p. 7243-7253Article in journal (Refereed)
    Abstract [en]

    We describe how inversion symmetry separation of electronic state manifolds in resonant inelastic soft X-ray scattering (RIXS) can be applied to probe excited-state dynamics with compelling selectivity. In a case study of Fe L-3-edge RIXS in the ferricyanide complex Fe(CN)(6)(3-), we demonstrate with multi-configurational restricted active space spectrum simulations how the information content of RIXS spectral fingerprints can be used to unambiguously separate species of different electronic configurations, spin multiplicities, and structures, with possible involvement in the decay dynamics of photo-excited ligand-to-metal charge-transfer. Specifically, we propose that this could be applied to confirm or reject the presence of a hitherto elusive transient Quartet species. Thus, RIXS offers a particular possibility to settle a recent controversy regarding the decay pathway, and we expect the technique to be similarly applicable in other model systems of photo-induced dynamics.

  • 8.
    Norell, Jesper
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Ljungdahl, Anton
    Stockholm University, Faculty of Science, Department of Physics.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Interdependent Electronic Structure, Protonation, and Solvatization of Aqueous 2-Thiopyridone2019In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 123, no 26, p. 5555-5567Article in journal (Refereed)
    Abstract [en]

    2-Thiopyridone (2-TP), a common model system for excited-state proton transfer, has been simulated in aqueous solution with ab initio molecular dynamics. The interplay of electronic structure, protonation, and solvatization is investigated by comparison of three differently protonated molecular forms and between the lowest singlet and triplet electronic states. An interdependence clearly manifests in the mixed-character T-1 state for the 2-TP form, systematic structural distortions of the 2-mercaptopyridine (2-MP) form, and photobase protolysis of the 2-TP- form, in the aqueous phase. In comparison, simplified continuum models for the solvatization are found to be significantly inaccurate for several of the species. To facilitate future computational studies, we therefore present a minimal representative solvatization complex for each stable form and electronic state. Our findings demonstrate the importance of explicit solvatization of the compound and sets the studies. stage for including it also in future studies.

1 - 8 of 8
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