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1. The Liquid Jet Endstation for Hard X-ray Scattering and Spectroscopy at the Linac Coherent Light Source.

Author

Antolini, Cali, Sosa Alfaro, Victor, Reinhard, Marco, Chatterjee, Gourab, Ribson, Ryan, Sokaras, Dimosthenis, Gee, Leland, Sato, Takahiro, Kramer, Patrick, Raj, Sumana, Hayes, Brandon, Schleissner, Pamela, Garcia-Esparza, Angel, Lim, Jinkyu, Babicz, Jeffrey, Follmer, Alec, Nelson, Silke, Chollet, Matthieu, Alonso-Mori, Roberto, and van Driel, Tim

Subjects
EXAFS, X-ray absorption spectroscopy, X-ray diffraction, X-ray emission spectroscopy, X-ray scattering, XANES, XFEL, biochemistry, photochemistry, time-resolved X-ray studies
Abstract

The ability to study chemical dynamics on ultrafast timescales has greatly advanced with the introduction of X-ray free electron lasers (XFELs) providing short pulses of intense X-rays tailored to probe atomic structure and electronic configuration. Fully exploiting the full potential of XFELs requires specialized experimental endstations along with the development of techniques and methods to successfully carry out experiments. The liquid jet endstation (LJE) at the Linac Coherent Light Source (LCLS) has been developed to study photochemistry and biochemistry in solution systems using a combination of X-ray solution scattering (XSS), X-ray absorption spectroscopy (XAS), and X-ray emission spectroscopy (XES). The pump-probe setup utilizes an optical laser to excite the sample, which is subsequently probed by a hard X-ray pulse to resolve structural and electronic dynamics at their intrinsic femtosecond timescales. The LJE ensures reliable sample delivery to the X-ray interaction point via various liquid jets, enabling rapid replenishment of thin samples with millimolar concentrations and low sample volumes at the 120 Hz repetition rate of the LCLS beam. This paper provides a detailed description of the LJE design and of the techniques it enables, with an emphasis on the diagnostics required for real-time monitoring of the liquid jet and on the spatiotemporal overlap methods used to optimize the signal. Additionally, various scientific examples are discussed, highlighting the versatility of the LJE.

Published
2024

2. Solution phase high repetition rate laser pump x-ray probe picosecond hard x-ray spectroscopy at the Stanford Synchrotron Radiation Lightsource.

Author

Reinhard, Marco, Skoien, Dean, Spies, Jacob, Garcia-Esparza, Angel, Matson, Benjamin, Corbett, Jeff, Tian, Kai, Safranek, James, Granados, Eduardo, Strader, Matthew, Gaffney, Kelly, Alonso-Mori, Roberto, Kroll, Thomas, and Sokaras, Dimosthenis

Abstract

We present a dedicated end-station for solution phase high repetition rate (MHz) picosecond hard x-ray spectroscopy at beamline 15-2 of the Stanford Synchrotron Radiation Lightsource. A high-power ultrafast ytterbium-doped fiber laser is used to photoexcite the samples at a repetition rate of 640 kHz, while the data acquisition operates at the 1.28 MHz repetition rate of the storage ring recording data in an alternating on-off mode. The time-resolved x-ray measurements are enabled via gating the x-ray detectors with the 20 mA/70 ps camshaft bunch of SPEAR3, a mode available during the routine operations of the Stanford Synchrotron Radiation Lightsource. As a benchmark study, aiming to demonstrate the advantageous capabilities of this end-station, we have conducted picosecond Fe K-edge x-ray absorption spectroscopy on aqueous [FeII(phen)3]2+, a prototypical spin crossover complex that undergoes light-induced excited spin state trapping forming an electronic excited state with a 0.6-0.7 ns lifetime. In addition, we report transient Fe Kβ main line and valence-to-core x-ray emission spectra, showing a unique detection sensitivity and an excellent agreement with model spectra and density functional theory calculations, respectively. Notably, the achieved signal-to-noise ratio, the overall performance, and the routine availability of the developed end-station have enabled a systematic time-resolved science program using the monochromatic beam at the Stanford Synchrotron Radiation Lightsource.

Published
2023

3. Ferricyanide photo-aquation pathway revealed by combined femtosecond Kβ main line and valence-to-core x-ray emission spectroscopy

Author

Reinhard, Marco, Gallo, Alessandro, Guo, Meiyuan, Garcia-Esparza, Angel T., Biasin, Elisa, Qureshi, Muhammad, Britz, Alexander, Ledbetter, Kathryn, Kunnus, Kristjan, Weninger, Clemens, van Driel, Tim, Robinson, Joseph, Glownia, James M., Gaffney, Kelly J., Kroll, Thomas, Weng, Tsu-Chien, Alonso-Mori, Roberto, and Sokaras, Dimosthenis

Published
2023
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4. Femtosecond X‑ray Spectroscopy Directly Quantifies Transient Excited-State Mixed Valency

Author

Liekhus-Schmaltz, Chelsea, Fox, Zachary W, Andersen, Amity, Kjaer, Kasper S, Alonso-Mori, Roberto, Biasin, Elisa, Carlstad, Julia, Chollet, Matthieu, Gaynor, James D, Glownia, James M, Hong, Kiryong, Kroll, Thomas, Lee, Jae Hyuk, Poulter, Benjamin I, Reinhard, Marco, Sokaras, Dimosthenis, Zhang, Yu, Doumy, Gilles, March, Anne Marie, Southworth, Stephen H, Mukamel, Shaul, Cordones, Amy A, Schoenlein, Robert W, Govind, Niranjan, and Khalil, Munira

Subjects
Inorganic Chemistry, Chemical Sciences, Physical Chemistry, Theoretical and Computational Chemistry, Physical Sciences, Chemical sciences, Physical sciences
Abstract

Quantifying charge delocalization associated with short-lived photoexcited states of molecular complexes in solution remains experimentally challenging, requiring local element specific femtosecond experimental probes of time-evolving electron transfer. In this study, we quantify the evolving valence hole charge distribution in the photoexcited charge transfer state of a prototypical mixed valence bimetallic iron-ruthenium complex, [(CN)5FeIICNRuIII(NH3)5]-, in water by combining femtosecond X-ray spectroscopy measurements with time-dependent density functional theory calculations of the excited-state dynamics. We estimate the valence hole charge that accumulated at the Fe atom to be 0.6 ± 0.2, resulting from excited-state metal-to-metal charge transfer, on an ∼60 fs time scale. Our combined experimental and computational approach provides a spectroscopic ruler for quantifying excited-state valency in solvated complexes.

Published
2022

5. Tuning Excited State Electron Transfer in Fe Tetracyano-Polypyridyl Complexes

Author

Kunnus, Kristjan, Li, Lin, Titus, Charles J., Lee, Sang Jun, Reinhard, Marco E., Koroidov, Sergey, Kjær, Kasper S., Hong, Kiryong, Ledbetter, Kathryn, Doriese, William B., O'Neil, Galen C., Swetz, Daniel S., Ullom, Joel N., Li, Dale, Irwin, Kent, Nordlund, Dennis, Cordones, Amy A., and Gaffney, Kelly J.

Subjects
Physics - Chemical Physics
Abstract

We have investigated photoinduced intramolecular electron transfer dynamics following metal-to-ligand charge-transfer (MLCT) excitation of [Fe(CN)$_4$(2,2'-bipyridine)]$^{2-}$ (1), [Fe(CN)$_4$(2,3-bis(2-pyridyl)pyrazine)]$^{2-}$ (2) and [Fe(CN)$_4$(2,2'-bipyrimidine)]$^{2-}$ (3) complexes in various solvents with static and time-resolved UV-visible absorption spectroscopy and Fe 2p3d resonant inelastic X-ray scattering. We observe $^3$MLCT lifetimes from 180 fs to 67 ps over a wide range of MLCT energies in different solvents by utilizing the strong solvatochromism of the complexes. Intramolecular electron transfer lifetimes governing $^3$MLCT relaxation increase monotonically and (super)exponentially as the $^3$MLCT energy is decreased in 1 and 2 by changing the solvent. This behavior can be described with non-adiabatic classical Marcus electron transfer dynamics along the indirect $^3$MLCT->$^3$MC pathway, where the $^3$MC is the lowest energy metal-centered (MC) excited state. In contrast, the $^3$MLCT lifetime in 3 changes non-monotonically and exhibits a maximum. This qualitatively different behaviour results from direct electron transfer from the $^3$MLCT to the electronic ground state (GS). This pathway involves nuclear tunnelling for the high-frequency polypyridyl skeleton mode ($\hbar\omega$ = 1530 cm$^{-1}$), which is more displaced for 3 than for either 1 or 2, therefore making the direct pathway significantly more efficient in 3. To our knowledge, this is the first observation of an efficient $^3$MLCT->GS relaxation pathway in an Fe polypyridyl complex. Our study suggests that further extending the MLCT state lifetime requires (1) lowering the $^3$MLCT state energy with respect to the $^3$MC state and (2) suppressing the intramolecular distortion of the electron-accepting ligand in the $^3$MLCT excited state to suppress the rate of direct $^3$MLCT->GS electron transfer.

Published
2019

6. Origin of vibrational wavepacket dynamics in Fe carbene photosensitizer determined with femtosecond X-ray emission and scattering

Author

Kunnus, Kristjan, Vacher, Morgane, Harlang, Tobias C. B., Kjær, Kasper S., Haldrup, Kristoffer, Biasin, Elisa, van Driel, Tim B., Pápa, Mátyás, Chabera, Pavel, Liu, Yizhu, Tatsuno, Hideyuki, Timm, Cornelia, Källman, Erik, Delcey, Mickaël, Hartsock, Robert W., Reinhard, Marco E., Koroidov, Sergey, Laursen, Mads G., Hansen, Frederik B., Vester, Peter, Christensen, Morten, Sandberg, Lise, Németh, Zoltán, Szemes, Dorottya Sárosiné, Bajnóczi, Éva, Alonso-Mori, Roberto, Glownia, James M., Nelson, Silke, Sikorski, Marcin, Sokaras, Dimosthenis, Lemke, Henrik T., Canton, Sophie, Møller, Klaus B., Nielsen, Martin M., Vankó, György, Wärnmark, Kenneth, Sundström, Villy, Persson, Petter, Lundberg, Marcus, Uhlig, Jens, and Gaffney, Kelly J.

Subjects
Physics - Chemical Physics
Abstract

Disentangling the dynamics of electrons and nuclei during nonadiabatic molecular transformations remains a considerable experimental challenge. Here we have investigated photoinduced electron transfer dynamics following a metal-to-ligand charge-transfer (MLCT) excitation of the [Fe(bmip)2]2+ photosensitizer, where bmip = 2,6-bis(3-methyl-imidazole-1- ylidine)-pyridine, with simultaneous femtosecond-resolution Fe K{\alpha} and K\b{eta} X-ray Emission Spectroscopy (XES) and Wide Angle X-ray Scattering (WAXS). This measurement clearly shows temporal oscillations in the XES and WAXS difference signals with the same 278 fs period oscillation. The oscillatory signal originates from an Fe-ligand stretching mode vibrational wavepacket on a triplet metal-centered (3MC) excited state surface. The vibrational wavepacket is created by 40% of the excited population that undergoes electron transfer from the non-equilibrium MLCT excited state to the 3MC excited state with a 110 fs time constant, while the other 60% relaxes to a 3MLCT excited state in parallel. The sensitivity of the K{\alpha} XES spectrum to molecular structure results from core-level vibronic coupling, due to a 0.7% average Fe-ligand bond length difference in the lowest energy geometry of the 1s and 2p core-ionized states. These results highlight the importance of vibronic effects in time-resolved XES experiments and demonstrate the role of metal-centered excited states in the electronic excited state relaxation dynamics of an Fe carbene photosensitizer.

Published
2019
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7. Observation of a Picosecond Light-Induced Spin Transition in Polymeric Nanorods

Author

Reinhard, Marco, primary, Kunnus, Kristjan, additional, Ledbetter, Kathryn, additional, Biasin, Elisa, additional, Zederkof, Diana Bregenholt, additional, Alonso-Mori, Roberto, additional, van Driel, Tim Brandt, additional, Nelson, Silke, additional, Kozina, Michael, additional, Borkiewicz, Olaf J., additional, Lorenc, Maciej, additional, Cammarata, Marco, additional, Collet, Eric, additional, Sokaras, Dimosthenis, additional, Cordones, Amy A., additional, and Gaffney, Kelly J., additional

Published
2024
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8. Direct observation of coherent femtosecond solvent reorganization coupled to intramolecular electron transfer

Author

Biasin, Elisa, Fox, Zachary W., Andersen, Amity, Ledbetter, Kathryn, Kjær, Kasper S., Alonso-Mori, Roberto, Carlstad, Julia M., Chollet, Matthieu, Gaynor, James D., Glownia, James M., Hong, Kiryong, Kroll, Thomas, Lee, Jae Hyuk, Liekhus-Schmaltz, Chelsea, Reinhard, Marco, Sokaras, Dimosthenis, Zhang, Yu, Doumy, Gilles, March, Anne Marie, Southworth, Stephen H., Mukamel, Shaul, Gaffney, Kelly J., Schoenlein, Robert W., Govind, Niranjan, Cordones, Amy A., and Khalil, Munira

Published
2021
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9. 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.

Author

Reinhard, Marco E., Sidhu, Baldeep K., Lozada, Issiah B., Powers-Riggs, Natalia, Ortiz, Robert J., Lim, Hyeongtaek, Nickel, Rachel, Lierop, Johan van, Alonso-Mori, Roberto, Chollet, Matthieu, Gee, Leland B., Kramer, Patrick L., Kroll, Thomas, Raj, Sumana L., van Driel, Tim B., Cordones, Amy A., Sokaras, Dimosthenis, Herbert, David E., and Gaffney, Kelly J.

Published
2024
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10. Ultrafast X-ray Absorption Spectroscopy Reveals Excited-State Dynamics of B12 Coenzymes Controlled by the Axial Base

Author

Chung, Taewon, primary, McClain, Taylor P., additional, Alonso-Mori, Roberto, additional, Chollet, Matthieu, additional, Deb, Aniruddha, additional, Garcia-Esparza, Angel T., additional, Huang Ze En, Joel, additional, Lamb, Ryan M., additional, Michocki, Lindsay B., additional, Reinhard, Marco, additional, van Driel, Tim B., additional, Penner-Hahn, James E., additional, and Sension, Roseanne J., additional

Published
2024
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11. Short-lived metal-centered excited state initiates iron-methionine photodissociation in ferrous cytochrome c

Author

Reinhard, Marco E., Mara, Michael W., Kroll, Thomas, Lim, Hyeongtaek, Hadt, Ryan G., Alonso-Mori, Roberto, Chollet, Matthieu, Glownia, James M., Nelson, Silke, Sokaras, Dimosthenis, Kunnus, Kristjan, Driel, Tim Brandt van, Hartsock, Robert W., Kjaer, Kasper S., Weninger, Clemens, Biasin, Elisa, Gee, Leland B., Hodgson, Keith O., Hedman, Britt, Bergmann, Uwe, Solomon, Edward I., and Gaffney, Kelly J.

Published
2021
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12. Author Correction: Direct observation of coherent femtosecond solvent reorganization coupled to intramolecular electron transfer

Author

Biasin, Elisa, Fox, Zachary W., Andersen, Amity, Ledbetter, Kathryn, Kjær, Kasper S., Alonso-Mori, Roberto, Carlstad, Julia M., Chollet, Matthieu, Gaynor, James D., Glownia, James M., Hong, Kiryong, Kroll, Thomas, Lee, Jae Hyuk, Liekhus-Schmaltz, Chelsea, Reinhard, Marco, Sokaras, Dimosthenis, Zhang, Yu, Doumy, Gilles, March, Anne Marie, Southworth, Stephen H., Mukamel, Shaul, Gaffney, Kelly J., Schoenlein, Robert W., Govind, Niranjan, Cordones, Amy A., and Khalil, Munira

Published
2022
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14. Vibrational wavepacket dynamics in Fe carbene photosensitizer determined with femtosecond X-ray emission and scattering

Author

Kunnus, Kristjan, Vacher, Morgane, Harlang, Tobias C. B., Kjær, Kasper S., Haldrup, Kristoffer, Biasin, Elisa, van Driel, Tim B., Pápai, Mátyás, Chabera, Pavel, Liu, Yizhu, Tatsuno, Hideyuki, Timm, Cornelia, Källman, Erik, Delcey, Mickaël, Hartsock, Robert W., Reinhard, Marco E., Koroidov, Sergey, Laursen, Mads G., Hansen, Frederik B., Vester, Peter, Christensen, Morten, Sandberg, Lise, Németh, Zoltán, Szemes, Dorottya Sárosiné, Bajnóczi, Éva, Alonso-Mori, Roberto, Glownia, James M., Nelson, Silke, Sikorski, Marcin, Sokaras, Dimosthenis, Lemke, Henrik T., Canton, Sophie E., Møller, Klaus B., Nielsen, Martin M., Vankó, György, Wärnmark, Kenneth, Sundström, Villy, Persson, Petter, Lundberg, Marcus, Uhlig, Jens, and Gaffney, Kelly J.

Published
2020
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16. Ultrafast X-ray Absorption Spectroscopy Reveals Excited-State Dynamics of B12Coenzymes Controlled by the Axial Base

Author

Chung, Taewon, McClain, Taylor P., Alonso-Mori, Roberto, Chollet, Matthieu, Deb, Aniruddha, Garcia-Esparza, Angel T., Huang Ze En, Joel, Lamb, Ryan M., Michocki, Lindsay B., Reinhard, Marco, van Driel, Tim B., Penner-Hahn, James E., and Sension, Roseanne J.

Abstract

Polarized time-resolved X-ray absorption spectroscopy at the Co K-edge is used to probe the excited-state dynamics and photolysis of base-off methylcobalamin and the excited-state structure of base-off adenosylcobalamin. For both molecules, the final excited-state minimum shows evidence for an expansion of the cavity around the Co ion by ca. 0.04 to 0.05 Å. The 5-coordinate base-off cob(II)alamin that is formed following photodissociation has a structure similar to that of the 5-coordinate base-on cob(II)alamin, with a ring expansion of 0.03 to 0.04 Å and a contraction of the lower axial bond length relative to that in the 6-coordinate ground state. These data provide insights into the role of the lower axial ligand in modulating the reactivity of B12coenzymes.

Published
2024
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19. Excited state charge distribution and bond expansion of ferrous complexes observed with femtosecond valence-to-core x-ray emission spectroscopy.

Author

Ledbetter, Kathryn, Reinhard, Marco E., Kunnus, Kristjan, Gallo, Alessandro, Britz, Alexander, Biasin, Elisa, Glownia, James M., Nelson, Silke, Van Driel, Tim B., Weninger, Clemens, Zederkof, Diana B., Haldrup, Kristoffer, Cordones, Amy A., Gaffney, Kelly J., Sokaras, Dimosthenis, and Alonso-Mori, Roberto

Subjects
*X-ray emission spectroscopy, *EXCITED states, *FREE electron lasers, *CHARGE transfer, *CHEMICAL bond lengths, *DENSITY functional theory
Abstract

Valence-to-core x-ray emission spectroscopy (VtC XES) combines the sample flexibility and element specificity of hard x-rays with the chemical environment sensitivity of valence spectroscopy. We extend this technique to study geometric and electronic structural changes induced by photoexcitation in the femtosecond time domain via laser-pump, x-ray probe experiments using an x-ray free electron laser. The results of time-resolved VtC XES on a series of ferrous complexes [Fe(CN)2n(2, 2′-bipyridine)3−n]−2n+2, n = 1, 2, 3, are presented. Comparisons of spectra obtained from ground state density functional theory calculations reveal signatures of excited state bond length and oxidation state changes. An oxidation state change associated with a metal-to-ligand charge transfer state with a lifetime of less than 100 fs is observed, as well as bond length changes associated with metal-centered excited states with lifetimes of 13 ps and 250 ps. [ABSTRACT FROM AUTHOR]

Published
2020
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20. Solvatochromic and Ligand Effects in Ultrafast Intramolecular Electron Transfer in Fe-based Molecular Photosensitizers

Author

Kunnus Kristjan, Li Lin, Reinhard Marco, Koroidov Sergey, Kjaer Kasper S., Ledbetter Kathryn, Hong Kiryong, Biasin Elisa, Cordones-Hahn Amy, and Gaffney Kelly J.

Subjects
Physics, QC1-999
Abstract

Metal-to-ligand charge-transfer (MLCT) excited state lifetimes of [Fe(CN)4(2,2’-bipyridine)]2- and [Fe(CN)4(2,3-bis(2-pyridyl)pyrazine)]2-exhibit strong solvent and ligand dependence. We conclude that these effects can be described with Marcus-like model where changes in the MLCT energy correspond directly to the changes in the electron transfer driving force and all the other factors (e.g. reorganization energy) can be considered constant.

Published
2019
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23. Femtosecond X-ray Spectroscopy Directly Quantifies Transient Excited State Mixed Valency and Subsequent Vibronic Dynamics

Author

Liekhus-Schmaltz, Chelsea, primary, Fox, Zachary, additional, Andersen, Amity, additional, Kjaer, Kasper, additional, Alonso-Mori, Roberto, additional, Biasin, Elisa, additional, Carlstad, Julia, additional, Chollet, Matthieu, additional, Gaynor, James, additional, Glownia, James, additional, Hong, Kiryong, additional, Kroll, Thomas, additional, Lee, Jae Hyuk, additional, Poulter, Benjamin, additional, Reinhard, Marco, additional, Sokaras, Dimosthenis, additional, Zhang, Yu, additional, Doumy, Gilles, additional, March, Anne-Marie, additional, Southworth, Stephen, additional, Mukamel, Shaul, additional, Cordones-Hahn, Amy, additional, Schoenlein, Robert, additional, Govind, Niranjan, additional, and Khalil, Munira, additional

Published
2021
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24. Operando Elucidation on the Working State of Immobilized Fluorinated Iron Porphyrin for Selective Aqueous Electroreduction of CO2 to CO

Author

Lu, Xiaofei, primary, Ahsaine, Hassan Ait, additional, Dereli, Busra, additional, Garcia-Esparza, Angel T., additional, Reinhard, Marco, additional, Shinagawa, Tatsuya, additional, Li, Duanxing, additional, Adil, Karim, additional, Tchalala, Mohamed Rachid, additional, Kroll, Thomas, additional, Eddaoudi, Mohamed, additional, Sokaras, Dimosthenis, additional, Cavallo, Luigi, additional, and Takanabe, Kazuhiro, additional

Published
2021
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25. Chemical control of competing electron transfer pathways in iron tetracyano-polypyridyl photosensitizers

Author

Kunnus, Kristjan, Li, Lin, Titus, Charles, Lee, Sang Jun, Reinhard, Marco E., Koroidov, Sergey, Kjaer, Kasper S., Hong, Kiryong, Ledbetter, Kathryn, Doriese, William B., O'Neil, Galen C., Swetz, Daniel S., Ullom, Joel, Li, Dale, Irwin, Kent, Nordlund, Dennis, Cordones, Amy, Gaffney, Kelly J., Kunnus, Kristjan, Li, Lin, Titus, Charles, Lee, Sang Jun, Reinhard, Marco E., Koroidov, Sergey, Kjaer, Kasper S., Hong, Kiryong, Ledbetter, Kathryn, Doriese, William B., O'Neil, Galen C., Swetz, Daniel S., Ullom, Joel, Li, Dale, Irwin, Kent, Nordlund, Dennis, Cordones, Amy, and Gaffney, Kelly J.

Abstract

Photoinduced intramolecular electron transfer dynamics following metal-to-ligand charge-transfer (MLCT) excitation of [Fe(CN)(4)(2,2 '-bipyridine)](2-) (1), [Fe(CN)(4)(2,3-bis(2-pyridyl)pyrazine)](2-) (2) and [Fe(CN)(4)(2,2 '-bipyrimidine)](2-) (3) were investigated in various solvents with static and time-resolved UV-Visible absorption spectroscopy and Fe 2p3d resonant inelastic X-ray scattering (RIXS). This series of polypyridyl ligands, combined with the strong solvatochromism of the complexes, enables the (MLCT)-M-1 vertical energy to be varied from 1.64 eV to 2.64 eV and the (MLCT)-M-3 lifetime to range from 180 fs to 67 ps. The (MLCT)-M-3 lifetimes in 1 and 2 decrease exponentially as the MLCT energy increases, consistent with electron transfer to the lowest energy triplet metal-centred ((MC)-M-3) excited state, as established by the Tanabe-Sugano analysis of the Fe 2p3d RIXS data. In contrast, the (MLCT)-M-3 lifetime in 3 changes non-monotonically with MLCT energy, exhibiting a maximum. This qualitatively distinct behaviour results from a competing (MLCT)-M-3 -> ground state (GS) electron transfer pathway that exhibits energy gap law behaviour. The (MLCT)-M-3 -> GS pathway involves nuclear tunnelling for the high-frequency polypyridyl breathing mode (h nu = 1530 cm(-1)), which is most displaced for complex 3, making this pathway significantly more efficient. Our study demonstrates that the excited state relaxation mechanism of Fe polypyridyl photosensitizers can be readily tuned by ligand and solvent environment. Furthermore, our study reveals that extending charge transfer lifetimes requires control of the relative energies of the (MLCT)-M-3 and the (MC)-M-3 states and suppression of the intramolecular distortion of the acceptor ligand in the (MLCT)-M-3 excited state.

Published
2020
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26. Hot branching dynamics in a light‐harvesting iron carbene complex revealed by ultrafast x‐ray emission spectroscopy

Author

Tatsuno, Hideyuki, Kjær, Kasper Skov, Kunnus, Kristjan, Harlang, Tobias C. B., Timm, Cornelia, Guo, Meiyuan, Chabera, Pavel, Fredin, Lisa A., Hartsock, Robert W., Reinhard, Marco E., Koroidov, Sergey, Li, Lin, Cordones, Amy, Gordivska, Olga, Prakash, Om, Liu, Yizhu, Laursen, Mads, Biasin, Elisa, Hansen, Frederik Beyer Kjær, Vester, Peter, Christensen, Morten, Haldrup, Kristoffer, Németh, Zoltán, Sárosiné Szemes, Dorottya, Bajnóczi, Éva, Vankó, György, van Driel, Tim B., Alonso-Mori, Roberto, Glownia, James, Nelson, Silke, Sikorski, Marcin, Lemke, Henrik Till, Sokaras, Dimosthenis, Canton, Sophie E., Dohn, Asmus Ougaard, Møller, Klaus Braagaard, Nielsen, Martin Meedom, Gaffney, Kelly J., Wärnmark, Kenneth, Sundström, Villy, Persson, Petter, Uhlig, Jens, Tatsuno, Hideyuki, Kjær, Kasper Skov, Kunnus, Kristjan, Harlang, Tobias C. B., Timm, Cornelia, Guo, Meiyuan, Chabera, Pavel, Fredin, Lisa A., Hartsock, Robert W., Reinhard, Marco E., Koroidov, Sergey, Li, Lin, Cordones, Amy, Gordivska, Olga, Prakash, Om, Liu, Yizhu, Laursen, Mads, Biasin, Elisa, Hansen, Frederik Beyer Kjær, Vester, Peter, Christensen, Morten, Haldrup, Kristoffer, Németh, Zoltán, Sárosiné Szemes, Dorottya, Bajnóczi, Éva, Vankó, György, van Driel, Tim B., Alonso-Mori, Roberto, Glownia, James, Nelson, Silke, Sikorski, Marcin, Lemke, Henrik Till, Sokaras, Dimosthenis, Canton, Sophie E., Dohn, Asmus Ougaard, Møller, Klaus Braagaard, Nielsen, Martin Meedom, Gaffney, Kelly J., Wärnmark, Kenneth, Sundström, Villy, Persson, Petter, and Uhlig, Jens

Abstract

Iron nitrogen heterocyclic carbenes (NHC) have received a great deal of attention recently, due to their growing potential as e.g light sensitizers and photocatalysts. We present a sub-ps x-ray spectroscopy study of a FeIINHC complex allowing us to identify and quantify the states involved in the deactivation cascade after light absorption. We find that excited molecules relax back to the ground state populating first the 3MLCT and then along two pathways the 3MC state. One of these pathways is ultrafast (~150 fs) for ~30% of the excited molecules, in competition with vibrational relaxation and cooling, followed by a much slower (7.6 ps) decay of the relaxed 3MLCT state. The 3MC state then rapidly (2.2 ps) decays to the ground state. The ultrafast deactivation of the 3MLCT state constitutes a loss channel from the point of view of photochemical efficiency and highlights the necessity to screen other FeNHC complexes (and perhaps other transition metal complexes) for this ultrafast decay of 3MLCT population, in order to optimize photochemical performance.

Published
2020

28. Author Correction: Direct observation of coherent femtosecond solvent reorganization coupled to intramolecular electron transfer

Author

Biasin, Elisa, primary, Fox, Zachary W., additional, Andersen, Amity, additional, Ledbetter, Kathryn, additional, Kjær, Kasper S., additional, Alonso-Mori, Roberto, additional, Carlstad, Julia M., additional, Chollet, Matthieu, additional, Gaynor, James D., additional, Glownia, James M., additional, Hong, Kiryong, additional, Kroll, Thomas, additional, Lee, Jae Hyuk, additional, Liekhus-Schmaltz, Chelsea, additional, Reinhard, Marco, additional, Sokaras, Dimosthenis, additional, Zhang, Yu, additional, Doumy, Gilles, additional, March, Anne Marie, additional, Southworth, Stephen H., additional, Mukamel, Shaul, additional, Gaffney, Kelly J., additional, Schoenlein, Robert W., additional, Govind, Niranjan, additional, Cordones, Amy A., additional, and Khalil, Munira, additional

Published
2021
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29. Resolving structures of transition metal complex reaction intermediates with femtosecond EXAFS

Author

Britz, Alexander, primary, Abraham, Baxter, additional, Biasin, Elisa, additional, van Driel, Tim Brandt, additional, Gallo, Alessandro, additional, Garcia-Esparza, Angel T., additional, Glownia, James, additional, Loukianov, Anton, additional, Nelson, Silke, additional, Reinhard, Marco, additional, Sokaras, Dimosthenis, additional, and Alonso-Mori, Roberto, additional

Published
2020
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30. Chemical control of competing electron transfer pathways in iron tetracyano-polypyridyl photosensitizers

Author

Kunnus, Kristjan, primary, Li, Lin, additional, Titus, Charles J., additional, Lee, Sang Jun, additional, Reinhard, Marco E., additional, Koroidov, Sergey, additional, Kjær, Kasper S., additional, Hong, Kiryong, additional, Ledbetter, Kathryn, additional, Doriese, William B., additional, O'Neil, Galen C., additional, Swetz, Daniel S., additional, Ullom, Joel N., additional, Li, Dale, additional, Irwin, Kent, additional, Nordlund, Dennis, additional, Cordones, Amy A., additional, and Gaffney, Kelly J., additional

Published
2020
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31. Ultrafast Charge Transfer and Electron Delocalization in a Cyanide-Bridged Ru-Ru Dimer Investigated with Femtosecond Transient X-Ray and IR Spectroscopies

Author

Poulter, Benjamin I., primary, Biasin, Elisa, additional, Liekhus-Schmaltz, Chelsea, additional, Arrell, Christopher, additional, Augustin, Sven, additional, Cirelli, Claudio, additional, Cordones-Hahn, Amy, additional, Johnson, Phillip, additional, Knopp, Gregor, additional, Milne, Christopher, additional, Mori, Roberto Alonso, additional, Ozerov, Dmitry, additional, Reinhard, Marco, additional, Sandwisch, Jason W., additional, Sokaras, Dimosthenis, additional, Usov, Ivan, additional, Weakly, Robert B., additional, Govind, Niranjan, additional, Schoenlein, Robert W., additional, and Khalil, Munira, additional

Published
2020
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32. Finding intersections between electronic excited state potential energy surfaces with simultaneous ultrafast X-ray scattering and spectroscopy

Author

Kjær, Kasper S., Van Driel, Tim B., Harlang, Tobias C.B., Kunnus, Kristjan, Biasin, Elisa, Ledbetter, Kathryn, Hartsock, Robert W., Reinhard, Marco E., Koroidov, Sergey, Li, Lin, Laursen, Mads G., Hansen, Frederik B., Vester, Peter, Christensen, Morten, Haldrup, Kristoffer, Nielsen, Martin M., Dohn, Asmus O., Pápai, Mátyás I., Møller, Klaus B., Chabera, Pavel, Liu, Yizhu, Tatsuno, Hideyuki, Timm, Cornelia, Jarenmark, Martin, Uhlig, Jens, Sundstöm, Villy, Wärnmark, Kenneth, Persson, Petter, Németh, Zoltán, Szemes, Dorottya Sárosiné, Bajnóczi, Éva, Vankó, György, Alonso-Mori, Roberto, Glownia, James M., Nelson, Silke, Sikorski, Marcin, Sokaras, Dimosthenis, Canton, Sophie E., Lemke, Henrik T., Gaffney, Kelly J., Kjær, Kasper S., Van Driel, Tim B., Harlang, Tobias C.B., Kunnus, Kristjan, Biasin, Elisa, Ledbetter, Kathryn, Hartsock, Robert W., Reinhard, Marco E., Koroidov, Sergey, Li, Lin, Laursen, Mads G., Hansen, Frederik B., Vester, Peter, Christensen, Morten, Haldrup, Kristoffer, Nielsen, Martin M., Dohn, Asmus O., Pápai, Mátyás I., Møller, Klaus B., Chabera, Pavel, Liu, Yizhu, Tatsuno, Hideyuki, Timm, Cornelia, Jarenmark, Martin, Uhlig, Jens, Sundstöm, Villy, Wärnmark, Kenneth, Persson, Petter, Németh, Zoltán, Szemes, Dorottya Sárosiné, Bajnóczi, Éva, Vankó, György, Alonso-Mori, Roberto, Glownia, James M., Nelson, Silke, Sikorski, Marcin, Sokaras, Dimosthenis, Canton, Sophie E., Lemke, Henrik T., and Gaffney, Kelly J.

Abstract

Light-driven molecular reactions are dictated by the excited state potential energy landscape, depending critically on the location of conical intersections and intersystem crossing points between potential surfaces where non-adiabatic effects govern transition probabilities between distinct electronic states. While ultrafast studies have provided significant insight into electronic excited state reaction dynamics, experimental approaches for identifying and characterizing intersections and seams between electronic states remain highly system dependent. Here we show that for 3d transition metal systems simultaneously recorded X-ray diffuse scattering and X-ray emission spectroscopy at sub-70 femtosecond time-resolution provide a solid experimental foundation for determining the mechanistic details of excited state reactions. In modeling the mechanistic information retrieved from such experiments, it becomes possible to identify the dominant trajectory followed during the excited state cascade and to determine the relevant loci of intersections between states. We illustrate our approach by explicitly mapping parts of the potential energy landscape dictating the light driven low-to-high spin-state transition (spin crossover) of [Fe(2,2′-bipyridine)3]2+, where the strongly coupled nuclear and electronic dynamics have been a source of interest and controversy. We anticipate that simultaneous X-ray diffuse scattering and X-ray emission spectroscopy will provide a valuable approach for mapping the reactive trajectories of light-triggered molecular systems involving 3d transition metals.

Published
2019

34. Hot Branching Dynamics in a Light‐Harvesting Iron Carbene Complex Revealed by Ultrafast X‐ray Emission Spectroscopy

Author

Tatsuno, Hideyuki, primary, Kjær, Kasper S., additional, Kunnus, Kristjan, additional, Harlang, Tobias C. B., additional, Timm, Cornelia, additional, Guo, Meiyuan, additional, Chàbera, Pavel, additional, Fredin, Lisa A., additional, Hartsock, Robert W., additional, Reinhard, Marco E., additional, Koroidov, Sergey, additional, Li, Lin, additional, Cordones, Amy A., additional, Gordivska, Olga, additional, Prakash, Om, additional, Liu, Yizhu, additional, Laursen, Mads G., additional, Biasin, Elisa, additional, Hansen, Frederik B., additional, Vester, Peter, additional, Christensen, Morten, additional, Haldrup, Kristoffer, additional, Németh, Zoltán, additional, Sárosiné Szemes, Dorottya, additional, Bajnóczi, Éva, additional, Vankó, György, additional, Van Driel, Tim B., additional, Alonso‐Mori, Roberto, additional, Glownia, James M., additional, Nelson, Silke, additional, Sikorski, Marcin, additional, Lemke, Henrik T., additional, Sokaras, Dimosthenis, additional, Canton, Sophie E., additional, Dohn, Asmus O., additional, Møller, Klaus B., additional, Nielsen, Martin M., additional, Gaffney, Kelly J., additional, Wärnmark, Kenneth, additional, Sundström, Villy, additional, Persson, Petter, additional, and Uhlig, Jens, additional

Published
2019
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36. Finding intersections between electronic excited state potential energy surfaces with simultaneous ultrafast X-ray scattering and spectroscopy

Author

Kjær, Kasper S., primary, Van Driel, Tim B., additional, Harlang, Tobias C. B., additional, Kunnus, Kristjan, additional, Biasin, Elisa, additional, Ledbetter, Kathryn, additional, Hartsock, Robert W., additional, Reinhard, Marco E., additional, Koroidov, Sergey, additional, Li, Lin, additional, Laursen, Mads G., additional, Hansen, Frederik B., additional, Vester, Peter, additional, Christensen, Morten, additional, Haldrup, Kristoffer, additional, Nielsen, Martin M., additional, Dohn, Asmus O., additional, Pápai, Mátyás I., additional, Møller, Klaus B., additional, Chabera, Pavel, additional, Liu, Yizhu, additional, Tatsuno, Hideyuki, additional, Timm, Cornelia, additional, Jarenmark, Martin, additional, Uhlig, Jens, additional, Sundstöm, Villy, additional, Wärnmark, Kenneth, additional, Persson, Petter, additional, Németh, Zoltán, additional, Szemes, Dorottya Sárosiné, additional, Bajnóczi, Éva, additional, Vankó, György, additional, Alonso-Mori, Roberto, additional, Glownia, James M., additional, Nelson, Silke, additional, Sikorski, Marcin, additional, Sokaras, Dimosthenis, additional, Canton, Sophie E., additional, Lemke, Henrik T., additional, and Gaffney, Kelly J., additional

Published
2019
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37. Coherent structural dynamics observed with femtosecond Fe K alpha and K beta X-ray emission spectroscopies

Author

Kunnus, Kristjan, Harlang, Tobias, Kjaer, Kasper Skov, Vacher, Morgane, Vanko, Gyorgy, Haldrup, Kristoffer, van Driel, Tim, Reinhard, Marco, Hartsock, Robert, Biasin, Elisa, Nielsen, Martin, Sundstrom, Villy, Lundberg, Marcus, Warnmark, Kenneth, Gaffney, Kelly, Kunnus, Kristjan, Harlang, Tobias, Kjaer, Kasper Skov, Vacher, Morgane, Vanko, Gyorgy, Haldrup, Kristoffer, van Driel, Tim, Reinhard, Marco, Hartsock, Robert, Biasin, Elisa, Nielsen, Martin, Sundstrom, Villy, Lundberg, Marcus, Warnmark, Kenneth, and Gaffney, Kelly

Published
2018

38. Probing the Electron Accepting Orbitals of Ni-Centered Hydrogen Evolution Catalysts with Noninnocent Ligands by Ni L-Edge and S K-Edge X-ray Absorption

Author

Koroidov, Sergey, Hong, Kiryong, Kjaer, Kasper S., Li, Lin, Kunnus, Kristjan, Reinhard, Marco, Hartsock, Robert W., Amit, Das, Eisenberg, Richard, Das Pemmaraju, C., Gaffney, Kelly J., Cordones, Amy A., Koroidov, Sergey, Hong, Kiryong, Kjaer, Kasper S., Li, Lin, Kunnus, Kristjan, Reinhard, Marco, Hartsock, Robert W., Amit, Das, Eisenberg, Richard, Das Pemmaraju, C., Gaffney, Kelly J., and Cordones, Amy A.

Abstract

The valence electronic structure of several square planar Ni-centered complexes, previously shown to catalyze the hydrogen evolution reaction, are characterized using S K-edge and Ni L-edge X-ray absorption spectroscopy and electronic structure calculations. Measurement of the atomic Ni 3d and S 3p contributions enables assessment of the metal-ligand covalency of the electron accepting valence orbitals and yields insight into the ligand-dependent reaction mechanisms proposed for the catalysts. The electron accepting orbital of the Ni(abt)(2) (abt = 2-aminobenzenethiolate) catalyst is found to have large ligand character (80%), with only 9% S 3p (per S) character, indicating delocalization over the entire abt ligand. Upon two proton-coupled reductions to form the Ni(abt-H)(2) intermediate, the catalyst stores 1.8 electrons on the abt ligand, and the ligand N atoms are protonated, thus supporting its role as an electron and proton reservoir. The electron accepting orbitals of the Ni(abt-H)(2) intermediate and Ni(mpo)(2) (mpo = 2-mercaptopyridyl-N-oxide) catalyst are found to have considerably larger Ni 3d (46-47%) and S 3p (17-18% per S) character, consistent with an orbital localized on the metal-ligand bonds. This finding supports the possibility of metal-based chemistry, resulting in Ni-H bond formation for the reduced Ni(abt-H)(2) intermediate and Ni(mpo)(2) catalyst, a critical reaction intermediate in H-2 generation.

Published
2018
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39. Solvent control of charge transfer excited state relaxation pathways in [Fe(2,2 '-bipyridine)(CN)4]2

Author

Kjær, Kasper Skov, Kunnus, Kristjan, Harlang, Tobias C. B., Van Driel, Tim B., Ledbetter, Kathryn, Hartsock, Robert W., Reinhard, Marco E., Koroidov, Sergey, Li, Lin, Laursen, Mads G., Biasin, Elisa, Hansen, Frederik B., Vester, Peter, Christensen, Morten, Haldrup, Kristoffer, Nielsen, Martin M., Chabera, Pavel, Liu, Yizhu, Tatsuno, Hideyuki, Timm, Cornelia, Uhlig, Jens, Sundstöm, Villy, Nemeth, Zoltan, Szemes, Dorottya Sarosine, Bajnoczi, Eva, Vanko, Gyorgy, Alonso-Mori, Roberto, Glownia, James M., Nelson, Silke, Sikorski, Marcin, Sokaras, Dimosthenis, Lemke, Henrik T., Canton, Sophie E., Warnmark, Kenneth, Persson, Petter, Cordones, Amy A., Gaffney, Kelly J., Kjær, Kasper Skov, Kunnus, Kristjan, Harlang, Tobias C. B., Van Driel, Tim B., Ledbetter, Kathryn, Hartsock, Robert W., Reinhard, Marco E., Koroidov, Sergey, Li, Lin, Laursen, Mads G., Biasin, Elisa, Hansen, Frederik B., Vester, Peter, Christensen, Morten, Haldrup, Kristoffer, Nielsen, Martin M., Chabera, Pavel, Liu, Yizhu, Tatsuno, Hideyuki, Timm, Cornelia, Uhlig, Jens, Sundstöm, Villy, Nemeth, Zoltan, Szemes, Dorottya Sarosine, Bajnoczi, Eva, Vanko, Gyorgy, Alonso-Mori, Roberto, Glownia, James M., Nelson, Silke, Sikorski, Marcin, Sokaras, Dimosthenis, Lemke, Henrik T., Canton, Sophie E., Warnmark, Kenneth, Persson, Petter, Cordones, Amy A., and Gaffney, Kelly J.

Abstract

The excited state dynamics of solvated [Fe(bpy)(CN)4]2-, where bpy = 2,2'-bipyridine, show significant sensitivity to the solvent Lewis acidity. Using a combination of optical absorption and X-ray emission transient spectroscopies, we have previously shown that the metal to ligand charge transfer (MLCT) excited state of [Fe(bpy)(CN)4]2- has a 19 picosecond lifetime and no discernable contribution from metal centered (MC) states in weak Lewis acid solvents, such as dimethyl sulfoxide and acetonitrile. 1,2 In the present work, we use the same combination of spectroscopic techniques to measure the MLCT excited state relaxation dynamics of [Fe(bpy)(CN)4]2- in water, a strong Lewis acid solvent. The charge-transfer excited state is now found to decay in less than 100 femtoseconds, forming a quasi-stable metal centered excited state with a 13 picosecond lifetime. We find that this MC excited state has triplet (3MC) character, unlike other reported six-coordinate Fe(II)-centered coordination compounds, which form MC quintet (5MC) states. The solvent dependent changes in excited state non-radiative relaxation for [Fe(bpy)(CN)4]2- allows us to infer the influence of the solvent on the electronic structure of the complex. Furthermore, the robust characterization of the dynamics and optical spectral signatures of the isolated 3MC intermediate provides a strong foundation for identifying 3MC intermediates in the electronic excited state relaxation mechanisms of similar Fe-centered systems being developed for solar applications.

Published
2018

40. Photoaquation mechanism of hexacyanoferrate(II) ions: ultrafast 2D UV and transient visible and IR spectroscopies

Author

Reinhard, Marco, Besley, Nicholas A., Clark, Ian P., Greetham, Gregory M., Hanson-Heine, Magnus W.D., Horvath, Raphael, Murphy, Thomas S., Penfold, Thomas J., Towrie, Michael, George, Michael W., and Chergui, Majed

Subjects
Physics::Chemical Physics
Abstract

Ferrous iron(II) hexacyanide in aqueous solutions is known to undergo photoionization and photoaquation reactions depending on the excitation wavelength. To investigate this wavelength dependence, we implemented ultrafast two-dimensional UV transient absorption spectroscopy, covering a range from 280 to 370 nm in both excitation and probing, along with UV pump/visible probe or time-resolved infrared (TRIR) transient absorption spectroscopy and density functional theory (DFT) calculations. As far as photoaquation is concerned, we find that excitation of the molecule leads to ultrafast intramolecular relaxation to the lowest triplet state of the [Fe(CN)6]4– complex, followed by its dissociation into CN– and [Fe(CN)5]3– fragments and partial geminate recombination, all within

Published
2017

41. Probing the Electron Accepting Orbitals of Ni-Centered Hydrogen Evolution Catalysts with Noninnocent Ligands by Ni L-Edge and S K-Edge X-ray Absorption

Author

Koroidov, Sergey, primary, Hong, Kiryong, additional, Kjaer, Kasper S., additional, Li, Lin, additional, Kunnus, Kristjan, additional, Reinhard, Marco, additional, Hartsock, Robert W., additional, Amit, Das, additional, Eisenberg, Richard, additional, Pemmaraju, C. Das, additional, Gaffney, Kelly J., additional, and Cordones, Amy A., additional

Published
2018
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43. Solvent control of charge transfer excited state relaxation pathways in [Fe(2,2′-bipyridine)(CN)4]2−

Author

Kjær, Kasper S., primary, Kunnus, Kristjan, additional, Harlang, Tobias C. B., additional, Van Driel, Tim B., additional, Ledbetter, Kathryn, additional, Hartsock, Robert W., additional, Reinhard, Marco E., additional, Koroidov, Sergey, additional, Li, Lin, additional, Laursen, Mads G., additional, Biasin, Elisa, additional, Hansen, Frederik B., additional, Vester, Peter, additional, Christensen, Morten, additional, Haldrup, Kristoffer, additional, Nielsen, Martin M., additional, Chabera, Pavel, additional, Liu, Yizhu, additional, Tatsuno, Hideyuki, additional, Timm, Cornelia, additional, Uhlig, Jens, additional, Sundstöm, Villy, additional, Németh, Zoltán, additional, Szemes, Dorottya Sárosiné, additional, Bajnóczi, Éva, additional, Vankó, György, additional, Alonso-Mori, Roberto, additional, Glownia, James M., additional, Nelson, Silke, additional, Sikorski, Marcin, additional, Sokaras, Dimosthenis, additional, Lemke, Henrik T., additional, Canton, Sophie E., additional, Wärnmark, Kenneth, additional, Persson, Petter, additional, Cordones, Amy A., additional, and Gaffney, Kelly J., additional

Published
2018
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45. Monitoring Excited State Charge Transfer of Transition Metal Mixed-Valence Complexes with Femtosecond X-ray Absorption and Emission Spectroscopy

Author

Fox, Zachary W., primary, Cordones-Hahn, Amy, additional, Kjær, Kasper S., additional, Gaynor, James D., additional, Hong, Kiryong, additional, Lee, Jae Hyuk, additional, Carlstad, Julia, additional, Reinhard, Marco, additional, Lee, Seunghee, additional, Alonso-Mori, Roberto, additional, Chollet, Matthieu, additional, Kroll, Thomas, additional, Glownia, James M., additional, Kim, Tae Kyu, additional, Andersen, Amity, additional, Zhang, Yu, additional, Mukamel, Shaul, additional, Govind, Niranjan, additional, Schoenlein, Robert W., additional, and Khalil, Munira, additional

Published
2016
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47. Solvent control of charge transfer excited state relaxation pathways in [Fe(2,2′-bipyridine)(CN)4]2−.

Author

Kjær, Kasper S., Kunnus, Kristjan, Harlang, Tobias C. B., Van Driel, Tim B., Ledbetter, Kathryn, Hartsock, Robert W., Reinhard, Marco E., Koroidov, Sergey, Li, Lin, Laursen, Mads G., Biasin, Elisa, Hansen, Frederik B., Vester, Peter, Christensen, Morten, Haldrup, Kristoffer, Nielsen, Martin M., Chabera, Pavel, Liu, Yizhu, Tatsuno, Hideyuki, and Timm, Cornelia

Abstract

The excited state dynamics of solvated [Fe(bpy)(CN)4]2−, where bpy = 2,2′-bipyridine, show significant sensitivity to the solvent Lewis acidity. Using a combination of optical absorption and X-ray emission transient spectroscopies, we have previously shown that the metal to ligand charge transfer (MLCT) excited state of [Fe(bpy)(CN)4]2− has a 19 picosecond lifetime and no discernable contribution from metal centered (MC) states in weak Lewis acid solvents, such as dimethyl sulfoxide and acetonitrile.1,2 In the present work, we use the same combination of spectroscopic techniques to measure the MLCT excited state relaxation dynamics of [Fe(bpy)(CN)4]2− in water, a strong Lewis acid solvent. The charge-transfer excited state is now found to decay in less than 100 femtoseconds, forming a quasi-stable metal centered excited state with a 13 picosecond lifetime. We find that this MC excited state has triplet (3MC) character, unlike other reported six-coordinate Fe(ii)-centered coordination compounds, which form MC quintet (5MC) states. The solvent dependent changes in excited state non-radiative relaxation for [Fe(bpy)(CN)4]2− allows us to infer the influence of the solvent on the electronic structure of the complex. Furthermore, the robust characterization of the dynamics and optical spectral signatures of the isolated 3MC intermediate provides a strong foundation for identifying 3MC intermediates in the electronic excited state relaxation mechanisms of similar Fe-centered systems being developed for solar applications. [ABSTRACT FROM AUTHOR]

Published
2018
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49. Probing the electronic and geometric structure of ferric and ferrous myoglobins in physiological solutions by Fe K-edge absorption spectroscopy

Author

Lima, Frederico A., primary, Penfold, Thomas J., additional, van der Veen, Renske M., additional, Reinhard, Marco, additional, Abela, Rafael, additional, Tavernelli, Ivano, additional, Rothlisberger, Ursula, additional, Benfatto, Maurizio, additional, Milne, Christopher J., additional, and Chergui, Majed, additional

Published
2014
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