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Reinhard ME, Sidhu BK, Lozada IB, Powers-Riggs N, Ortiz RJ, Lim H, Nickel R, Lierop JV, Alonso-Mori R, Chollet M, Gee LB, Kramer PL, Kroll T, Raj SL, van Driel TB, Cordones AA, Sokaras D, Herbert DE, Gaffney KJ. Time-Resolved X-ray Emission Spectroscopy and Synthetic High-Spin Model Complexes Resolve Ambiguities in Excited-State Assignments of Transition-Metal Chromophores: A Case Study of Fe-Amido Complexes. J Am Chem Soc 2024. [PMID: 38889309 DOI: 10.1021/jacs.4c02748] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/20/2024]
Abstract
To fully harness the potential of abundant metal coordination complex photosensitizers, a detailed understanding of the molecular properties that dictate and control the electronic excited-state population dynamics initiated by light absorption is critical. In the absence of detectable luminescence, optical transient absorption (TA) spectroscopy is the most widely employed method for interpreting electron redistribution in such excited states, particularly for those with a charge-transfer character. The assignment of excited-state TA spectral features often relies on spectroelectrochemical measurements, where the transient absorption spectrum generated by a metal-to-ligand charge-transfer (MLCT) electronic excited state, for instance, can be approximated using steady-state spectra generated by electrochemical ligand reduction and metal oxidation and accounting for the loss of absorptions by the electronic ground state. However, the reliability of this approach can be clouded when multiple electronic configurations have similar optical signatures. Using a case study of Fe(II) complexes supported by benzannulated diarylamido ligands, we highlight an example of such an ambiguity and show how time-resolved X-ray emission spectroscopy (XES) measurements can reliably assign excited states from the perspective of the metal, particularly in conjunction with accurate synthetic models of ligand-field electronic excited states, leading to a reinterpretation of the long-lived excited state as a ligand-field metal-centered quintet state. A detailed analysis of the XES data on the long-lived excited state is presented, along with a discussion of the ultrafast dynamics following the photoexcitation of low-spin Fe(II)-Namido complexes using a high-spin ground-state analogue as a spectral model for the 5T2 excited state.
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Affiliation(s)
- Marco E Reinhard
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - Baldeep K Sidhu
- Department of Chemistry and the Manitoba Institute for Materials, University of Manitoba, 144 Dysart Rd, Winnipeg, Manitoba R3T 2N2, Canada
| | - Issiah B Lozada
- Department of Chemistry and the Manitoba Institute for Materials, University of Manitoba, 144 Dysart Rd, Winnipeg, Manitoba R3T 2N2, Canada
| | - Natalia Powers-Riggs
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - Robert J Ortiz
- Department of Chemistry and the Manitoba Institute for Materials, University of Manitoba, 144 Dysart Rd, Winnipeg, Manitoba R3T 2N2, Canada
| | - Hyeongtaek Lim
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - Rachel Nickel
- Department of Physics and Astronomy, University of Manitoba, 31A Sifton Rd, Winnipeg, Manitoba R3T 2N2, Canada
| | - Johan van Lierop
- Department of Physics and Astronomy, University of Manitoba, 31A Sifton Rd, Winnipeg, Manitoba R3T 2N2, Canada
| | - Roberto Alonso-Mori
- Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - Matthieu Chollet
- Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - Leland B Gee
- Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - Patrick L Kramer
- Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - Thomas Kroll
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - Sumana L Raj
- Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - Tim B van Driel
- Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - Amy A Cordones
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - Dimosthenis Sokaras
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - David E Herbert
- Department of Chemistry and the Manitoba Institute for Materials, University of Manitoba, 144 Dysart Rd, Winnipeg, Manitoba R3T 2N2, Canada
| | - Kelly J Gaffney
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
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2
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Wallick R, Chakrabarti S, Burke JH, Gnewkow R, Chae JB, Rossi TC, Mantouvalou I, Kanngießer B, Fondell M, Eckert S, Dykstra C, Smith LE, Vura-Weis J, Mirica LM, van der Veen RM. Excited-State Identification of a Nickel-Bipyridine Photocatalyst by Time-Resolved X-ray Absorption Spectroscopy. J Phys Chem Lett 2024; 15:4976-4982. [PMID: 38691639 PMCID: PMC11089568 DOI: 10.1021/acs.jpclett.4c00226] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2024] [Revised: 03/18/2024] [Accepted: 04/16/2024] [Indexed: 05/03/2024]
Abstract
Photoassisted catalysis using Ni complexes is an emerging field for cross-coupling reactions in organic synthesis. However, the mechanism by which light enables and enhances the reactivity of these complexes often remains elusive. Although optical techniques have been widely used to study the ground and excited states of photocatalysts, they lack the specificity to interrogate the electronic and structural changes at specific atoms. Herein, we report metal-specific studies using transient Ni L- and K-edge X-ray absorption spectroscopy of a prototypical Ni photocatalyst, (dtbbpy)Ni(o-tol)Cl (dtb = 4,4'-di-tert-butyl, bpy = bipyridine, o-tol = ortho-tolyl), in solution. We unambiguously confirm via direct experimental evidence that the long-lived (∼5 ns) excited state is a tetrahedral metal-centered triplet state. These results demonstrate the power of ultrafast X-ray spectroscopies to unambiguously elucidate the nature of excited states in important transition-metal-based photocatalytic systems.
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Affiliation(s)
- Rachel
F. Wallick
- Department
of Chemistry, University of Illinois at
Urbana—Champaign, Urbana, Illinois 61801, United States
| | - Sagnik Chakrabarti
- Department
of Chemistry, University of Illinois at
Urbana—Champaign, Urbana, Illinois 61801, United States
| | - John H. Burke
- Department
of Chemistry, University of Illinois at
Urbana—Champaign, Urbana, Illinois 61801, United States
| | - Richard Gnewkow
- Department
of Atomic-Scale Dynamics in Light-Energy Conversion, Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin 14109, Germany
- Institute
of Optics and Atomic Physics, Technische
Universität Berlin, Berlin 10623, Germany
| | - Ju Byeong Chae
- Department
of Chemistry, University of Illinois at
Urbana—Champaign, Urbana, Illinois 61801, United States
| | - Thomas C. Rossi
- Department
of Atomic-Scale Dynamics in Light-Energy Conversion, Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin 14109, Germany
| | - Ioanna Mantouvalou
- Department
of Atomic-Scale Dynamics in Light-Energy Conversion, Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin 14109, Germany
- Institute
of Optics and Atomic Physics, Technische
Universität Berlin, Berlin 10623, Germany
| | - Birgit Kanngießer
- Department
of Atomic-Scale Dynamics in Light-Energy Conversion, Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin 14109, Germany
- Institute
of Optics and Atomic Physics, Technische
Universität Berlin, Berlin 10623, Germany
| | - Mattis Fondell
- Department
of Atomic-Scale Dynamics in Light-Energy Conversion, Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin 14109, Germany
| | - Sebastian Eckert
- Department
of Atomic-Scale Dynamics in Light-Energy Conversion, Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin 14109, Germany
| | - Conner Dykstra
- Department
of Chemistry, University of Illinois at
Urbana—Champaign, Urbana, Illinois 61801, United States
| | - Laura E. Smith
- Department
of Chemistry, University of Illinois at
Urbana—Champaign, Urbana, Illinois 61801, United States
| | - Josh Vura-Weis
- Department
of Chemistry, University of Illinois at
Urbana—Champaign, Urbana, Illinois 61801, United States
| | - Liviu M. Mirica
- Department
of Chemistry, University of Illinois at
Urbana—Champaign, Urbana, Illinois 61801, United States
| | - Renske M. van der Veen
- Department
of Chemistry, University of Illinois at
Urbana—Champaign, Urbana, Illinois 61801, United States
- Department
of Atomic-Scale Dynamics in Light-Energy Conversion, Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin 14109, Germany
- Institute
of Optics and Atomic Physics, Technische
Universität Berlin, Berlin 10623, Germany
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3
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Wegeberg C, Häussinger D, Kupfer S, Wenger OS. Controlling the Photophysical Properties of a Series of Isostructural d 6 Complexes Based on Cr 0, Mn I, and Fe II. J Am Chem Soc 2024; 146:4605-4619. [PMID: 38334415 PMCID: PMC10885143 DOI: 10.1021/jacs.3c11580] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/10/2024]
Abstract
Development of first-row transition metal complexes with similar luminescence and photoredox properties as widely used RuII polypyridines is attractive because metals from the first transition series are comparatively abundant and inexpensive. The weaker ligand field experienced by the valence d-electrons of first-row transition metals challenges the installation of the same types of metal-to-ligand charge transfer (MLCT) excited states as in precious metal complexes, due to rapid population of energetically lower-lying metal-centered (MC) states. In a family of isostructural tris(diisocyanide) complexes of the 3d6 metals Cr0, MnI, and FeII, the increasing effective nuclear charge and ligand field strength allow us to control the energetic order between the 3MLCT and 3MC states, whereas pyrene decoration of the isocyanide ligand framework provides control over intraligand (ILPyr) states. The chromium(0) complex shows red 3MLCT phosphorescence because all other excited states are higher in energy. In the manganese(I) complex, a microsecond-lived dark 3ILPyr state, reminiscent of the types of electronic states encountered in many polyaromatic hydrocarbon compounds, is the lowest and becomes photoactive. In the iron(II) complex, the lowest MLCT state has shifted to so much higher energy that 1ILPyr fluorescence occurs, in parallel to other excited-state deactivation pathways. Our combined synthetic-spectroscopic-theoretical study provides unprecedented insights into how effective nuclear charge, ligand field strength, and ligand π-conjugation affect the energetic order between MLCT and ligand-based excited states, and under what circumstances these individual states become luminescent and exploitable in photochemistry. Such insights are the key to further developments of luminescent and photoredox-active first-row transition metal complexes.
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Affiliation(s)
- Christina Wegeberg
- Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056 Basel, Switzerland
| | - Daniel Häussinger
- Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056 Basel, Switzerland
| | - Stephan Kupfer
- Institute of Physical Chemistry, Friedrich Schiller University Jena, Helmholtzweg 4, 07743 Jena, Germany
| | - Oliver S Wenger
- Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056 Basel, Switzerland
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4
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Deorukhkar N, Egger C, Guénée L, Besnard C, Piguet C. Detecting Fe(II) Spin-Crossover by Modulation of Appended Eu(III) Luminescence in a Single Molecule. J Am Chem Soc 2024; 146:308-318. [PMID: 37877700 DOI: 10.1021/jacs.3c09017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2023]
Abstract
Multifunctionality in spin-crossover (SCO) devices is limited to macroscopic or nanoscopic materials because of the need for long-range effects for inducing favorable cooperativity, efficient energy migration processes, and detectable magnetization transfer. The difficult reproducibility, control, and rational design of doped materials offer some place to SCO processes, modulating the optical properties of neighboring luminescent probes in single molecules. We report here on the combination of a [FeN6] chromophore, the SCO temperature and absorption spectra of which have been tuned to induce unprecedented room-temperature modulation of Eu(III)-based line-like luminescence in the molecular triple-helical [EuFe(L2)3]5+ complex in solution.
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Affiliation(s)
- Neel Deorukhkar
- Department of Inorganic and Analytical Chemistry, University of Geneva, 30 quai E. Ansermet, CH-1211 Geneva 4, Switzerland
| | - Charlotte Egger
- Department of Inorganic and Analytical Chemistry, University of Geneva, 30 quai E. Ansermet, CH-1211 Geneva 4, Switzerland
| | - Laure Guénée
- Laboratory of Crystallography, University of Geneva, 24 quai E. Ansermet. CH-1211 Geneva 4, Switzerland
| | - Céline Besnard
- Laboratory of Crystallography, University of Geneva, 24 quai E. Ansermet. CH-1211 Geneva 4, Switzerland
| | - Claude Piguet
- Department of Inorganic and Analytical Chemistry, University of Geneva, 30 quai E. Ansermet, CH-1211 Geneva 4, Switzerland
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5
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Barker M, Whittemore TJ, London HC, Sledesky JM, Harris EA, Smith Pellizzeri TM, McMillen CD, Wagenknecht PS. Design Strategies for Luminescent Titanocenes: Improving the Photoluminescence and Photostability of Arylethynyltitanocenes. Inorg Chem 2023; 62:17870-17882. [PMID: 37831503 PMCID: PMC10618925 DOI: 10.1021/acs.inorgchem.3c02712] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2023] [Indexed: 10/14/2023]
Abstract
Complexes that undergo ligand-to-metal charge transfer (LMCT) to d0 metals are of interest as possible photocatalysts. Cp2Ti(C2Ph)2 (where C2Ph = phenylethynyl) was reported to be weakly emissive in room-temperature (RT) fluid solution from its phenylethynyl-to-Ti 3LMCT state but readily photodecomposes. Coordination of CuX between the alkyne ligands to give Cp2Ti(C2Ph)2CuX (X = Cl, Br) has been shown to significantly increase the photostability, but such complexes are not emissive in RT solution. Herein, we investigate whether inhibition of alkyne-Ti-alkyne bond compression might be responsible for the increased photostability of the CuX complexes by investigating the decomposition of a structurally constrained analogue, Cp2Ti(OBET) (OBET = o-bis(ethynyl)tolane). To investigate the mechanism of nonradiative decay from the 3LMCT states in Cp2Ti(C2Ph)2CuX, the photophysical properties were investigated both upon deuteration and upon rigidifying in a poly(methyl methacrylate) film. These investigations suggested that inhibition of structural rearrangement may play a dominant role in increasing emission lifetimes and quantum yields. The bulkier Cp*2Ti(C2Ph)2CuBr was prepared and is emissive at 693 nm in RT THF solution with a photoluminescent quantum yield of 1.3 × 10-3 (τ = 0.18 μs). Time-dependent density functional theory (TDDFT) calculations suggest that emission occurs from a 3LMCT state dominated by Cp*-to-Ti charge transfer.
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Affiliation(s)
- Matilda Barker
- Department
of Chemistry, Furman University, Greenville, South Carolina 29609, United States
| | - Thomas J. Whittemore
- Department
of Chemistry, Furman University, Greenville, South Carolina 29609, United States
| | - Henry C. London
- Department
of Chemistry, Furman University, Greenville, South Carolina 29609, United States
| | - Jack M. Sledesky
- Department
of Chemistry, Furman University, Greenville, South Carolina 29609, United States
| | - Elizabeth A. Harris
- Department
of Chemistry, Furman University, Greenville, South Carolina 29609, United States
| | - Tiffany M. Smith Pellizzeri
- Department
of Chemistry and Biochemistry, Eastern Illinois
University, Charleston, Illinois 61920, United States
| | - Colin D. McMillen
- Department
of Chemistry, Clemson University, Clemson, South Carolina 29634, United States
| | - Paul S. Wagenknecht
- Department
of Chemistry, Furman University, Greenville, South Carolina 29609, United States
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6
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Wang C, Wegeberg C, Wenger OS. First-Row d 6 Metal Complex Enables Photon Upconversion and Initiates Blue Light-Dependent Polymerization with Red Light. Angew Chem Int Ed Engl 2023; 62:e202311470. [PMID: 37681516 DOI: 10.1002/anie.202311470] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2023] [Revised: 09/07/2023] [Accepted: 09/08/2023] [Indexed: 09/09/2023]
Abstract
Photosensitizers for sensitized triplet-triplet annihilation upconversion (sTTA-UC) often rely on precious heavy metals, whereas coordination complexes based on abundant first-row transition metals are less common. This is mainly because long-lived triplet excited states are more difficult to obtain for 3d metals, particularly when the d-subshell is only partially filled. Here, we report the first example of sTTA-UC based on a 3d6 metal photosensitizer yielding an upconversion performance competitive with precious metal-based analogues. Using a newly developed Cr0 photosensitizer featuring equally good photophysical properties as an OsII benchmark complex in combination with an acetylene-decorated anthracene annihilator, red-to-blue upconversion is achievable. The upconversion efficiency under optimized conditions is 1.8 %, and the excitation power density threshold to reach the strong annihilation limit is 5.9 W/cm2 . These performance factors, along with high photostability, permit the initiation of acrylamide polymerization by red light, based on radiative energy transfer between delayed annihilator fluorescence and a blue light absorbing photo-initiator. Our study provides the proof-of-concept for photon upconversion with elusive first-row analogues of widely employed precious d6 metal photosensitizers, and for their application in photochemical reactions triggered by excitation wavelengths close to near-infrared.
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Affiliation(s)
- Cui Wang
- Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056, Basel, Switzerland
- Current address: Department of Biology and Chemistry, Osnabrück University, Barbarastraße 7, 49076, Osnabrück, Germany
| | - Christina Wegeberg
- Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056, Basel, Switzerland
- Current address: Division of Chemical Physics, Department of Chemistry, Lund University Box 124, 22100, Lund, Sweden
| | - Oliver S Wenger
- Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056, Basel, Switzerland
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