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Ultrafast dynamics of two copper bis-phenanthroline complexes measured by x-ray transient absorption spectroscopy

Kelley, Matthew S. and Shelby, Megan L. and Mara, Michael W. and Haldrup, Kristoffer and Hayes, Dugan and Hadt, Ryan G. and Zhang, Xiaoyi and Stickrath, Andrew B. and Ruppert, Romain and Sauvage, Jean-Pierre and Zhu, Diling and Lemke, Henrik T. and Chollet, Matthieu and Schatz, George C. and Chen, Lin X. (2017) Ultrafast dynamics of two copper bis-phenanthroline complexes measured by x-ray transient absorption spectroscopy. Journal of Physics B: Atomic, Molecular and Optical Physics, 50 (15). Art. No. 154006. ISSN 0953-4075.

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Ultrafast structural dynamics of the metal to ligand charge transfer (MLCT) states of two copper bis-phenanthroline complexes were captured by using x-ray transient absorption (XTA) spectroscopy at the Linac Coherent Light Source and further described by theoretical calculations. These complexes have the general formula [Cu(I)(R)_2]+, where R = 2,9-dimethyl-1,10-phenanthroline (dmp) and 2,9-diphenyl-1,10-phenanthroline disulfonic acid disodium salt (dpps). [Cu(I)(dmp)_2]+ has methyl groups at the 2,9 positions of phenanthroline (phen) and adopts a pseudo-tetrahedral geometry. In contrast, [Cu(I)(dpps)_2]+ possesses two bulky phenyl-sulfonate groups attached to each phen ligand that force the molecule to adopt a flattened tetrahedral geometry in the ground state. Previously, optical transient absorption (OTA) and synchrotron based XTA experiments with 100 ps time resolution have been employed to study the relationship between structural distortions and excited state relaxation pathways in the two complexes. However, the dynamics of the MLCT transition during the first few picoseconds after excitation in these complexes remained unclear because of limitations in element specificity in OTA and in the time resolution of synchrotron sources in XTA. In this experiment, the local coordination geometry and oxidation state of copper were probed with a temporal resolution of ~300 fs. Unexpectedly, the depletion of the Cu(I) signal due to the MLCT transition was found to be non-impulsive in the case of [Cu(I)(dpps)_2]+ with a time constant of 0.6 ps, while the Cu(I) depletion in [Cu(I)(dmp)_2]+ was instantaneous within the 300 fs instrument response time. The slower Cu(I) depletion kinetics in [Cu(I)(dpps)_2]+, previously unobserved in femtosecond OTA experiments, is likely due to intramolecular motions on the sub-picosecond time scale that could alter the localization of the transferred electron in the phen ligands.

Item Type:Article
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URLURL TypeDescription
Haldrup, Kristoffer0000-0002-0565-6397
Hadt, Ryan G.0000-0001-6026-1358
Additional Information:© 2017 IOP Publishing Ltd. Received 27 March 2017, revised 11 June 2017; Accepted for publication 26 June 2017; Published 12 July 2017. We acknowledge support for this work from the Solar Energy Photochemistry program and Ultrafast Initiative of the US Department of Energy, Office of Science, Office of Basic Energy Sciences, through Argonne National Laboratory (ANL) under Contract No. DE-AC02-06CH11357. Use of the Linac Coherent Light Source (LCLS), SLAC National Accelerator Laboratory and Advanced Photon Source are, respectively, supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515 (LCLS) and DE-AC02-06CH11357 (APS). MSK is grateful for support from the National Defense Science and Engineering Graduate (NDSEG) Fellowship. DKH acknowledges J J Katz Postdoctoral Fellowship from ANL. RGH is an Enrico Fermi Fellow at ANL. KH gratefully acknowledges support from DANSCATT and from the Villum and Carlsberg Foundations. The authors would like to thank Tim Brandt Van Driel for invaluable assistance with the phase cavity timing correction by providing a means to calibrate the phase cavity data.
Funding AgencyGrant Number
Department of Energy (DOE)DE-AC02-06CH11357
Department of Energy (DOE)DE-AC02-76SF00515
National Defense Science and Engineering Graduate (NDSEG) FellowshipUNSPECIFIED
Argonne National LaboratoryUNSPECIFIED
Villum FoundationUNSPECIFIED
Carlsberg FoundationUNSPECIFIED
Issue or Number:15
Record Number:CaltechAUTHORS:20180612-074847743
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Official Citation:Matthew S Kelley et al 2017 J. Phys. B: At. Mol. Opt. Phys. 50 154006
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:86984
Deposited By: Tony Diaz
Deposited On:12 Jun 2018 15:04
Last Modified:03 Oct 2019 19:50

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