Ultrafast Excited State Relaxation of a Metalloporphyrin Revealed by Femtosecond X-ray Absorption Spectroscopy

Research output: Contribution to journalJournal article – Annual report year: 2016Researchpeer-review

Documents

DOI

  • Author: Shelby, Megan L.

    Argonne National Laboratory, United States

  • Author: Lestrange, Patrick J

    University of Washington, United States

  • Author: Jackson, Nicholas E

    Northwestern University, United States

  • Author: Haldrup, Kristoffer

    Neutrons and X-rays for Materials Physics, Department of Physics, Technical University of Denmark, Fysikvej, 2800, Kgs. Lyngby, Denmark

  • Author: Mara, Michael W.

    Northwestern University, United States

  • Author: Stickrath, Andrew B.

    Argonne National Laboratory, United States

  • Author: Zhu, Diling

    SLAC National Accelerator Laboratory, United States

  • Author: Lemke, Henrik Till

    SLAC National Accelerator Laboratory, United States

  • Author: Chollet, Matthieu

    SLAC National Accelerator Laboratory, United States

  • Author: Hoffman, Brian M

    Northwestern University, United States

  • Author: Li, Xiaosong

    University of Washington, United States

  • Author: Chen, Lin X.

    Argonne National Laboratory, United States

View graph of relations

Photoexcited Nickel(II) tetramesitylporphyrin (NiTMP), like many open-shell metalloporphyrins, relaxes rapidly through multiple electronic states following an initial porphyrin-based excitation, some involving metal centered electronic configuration changes that could be harnessed catalytically before excited state relaxation. While a NiTMP excited state present at 100 ps was previously identified by X-ray transient absorption (XTA) spectroscopy at a synchrotron source as a relaxed (d,d) state, the lowest energy excited state (J. Am. Chem. Soc., 2007, 129, 9616 and Chem. Sci., 2010, 1, 642), structural dynamics before thermalization were not resolved due to the similar to 100 ps duration of the available X-ray probe pulse. Using the femtosecond (fs) X-ray pulses of the Linac Coherent Light Source (LCLS), the Ni center electronic configuration from the initial excited state to the relaxed (d,d) state has been obtained via ultrafast Ni K-edge XANES (X-ray absorption near edge structure) on a time scale from hundreds of femtoseconds to 100 ps. This enabled the identification of a short-lived Ni(I) species aided by time-dependent density functional theory (TDDFT) methods. Computed electronic and nuclear structure for critical excited electronic states in the relaxation pathway characterize the dependence of the complex's geometry on the electron occupation of the 3d orbitals. Calculated XANES transitions for these excited states assign a short-lived transient signal to the spectroscopic signature of the Ni(I) species, resulting from intramolecular charge transfer on a time scale that has eluded previous synchrotron studies. These combined results enable us to examine the excited state structural dynamics of NiTMP prior to thermal relaxation and to capture intermediates of potential photocatalytic significance.
Original languageEnglish
JournalJournal of the American Chemical Society
Volume138
Issue number28
Pages (from-to)8752-8764
Number of pages13
ISSN0002-7863
DOIs
Publication statusPublished - 2016
CitationsWeb of Science® Times Cited: No match on DOI

Download statistics

No data available

ID: 128046620