Tracking the picosecond deactivation dynamics of a photoexcited iron carbene complex by time-resolved X-ray scattering

Denis Leshchev*, Tobias C. B. Harlang, Lisa A. Fredin, Dmitry Khakhulin, Yizhu Liu, Elisa Biasin, Mads G. Laursen, Gemma E. Newby, Kristoffer Haldrup, Martin Meedom Nielsen, Kenneth Warnmark, Villy Sundstrom, Petter Persson, Kasper Skov Kjær, Michael Wulff

*Corresponding author for this work

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Abstract

Recent years have seen the development of new iron-centered N-heterocyclic carbene (NHC) complexes for solar energy applications. Compared to typical ligand systems, the NHC ligands provide Fe complexes with longer-lived metal-to-ligand charge transfer (MLCT) states. This increased lifetime is ascribed to strong ligand field splitting provided by the NHC ligands that raises the energy levels of the metal centered (MC) states and therefore reduces the deactivation efficiency of MLCT states. Among currently known NHC systems, [Fe(btbip)2]2+ (btbip = 2,6-bis(3-tert-butyl-imidazol-1-ylidene)pyridine) is a unique complex as it exhibits a short-lived MC state with a lifetime on the scale of a few hundreds of picoseconds. Hence, this complex allows for a detailed investigation, using 100 ps X-ray pulses from a synchrotron, of strong ligand field effects on the intermediate MC state in an NHC complex. Here, we use time-resolved wide angle X-ray scattering (TRWAXS) aided by density functional theory (DFT) to investigate the molecular structure, energetics and lifetime of the high-energy MC state in the Fe-NHC complex  [Fe(btbip)2]2+ after excitation to the MLCT manifold. We identify it as a 260 ps metal-centered quintet (5MC) state, and we refine the molecular structure of the excited-state complex verifying the DFT results. Using information about the hydrodynamic state of the solvent, we also determine, for the first time, the energy of the 5MC state as 0.75 + 0.15 eV. Our results demonstrate that due to the increased ligand field strength caused by NHC ligands, upon transition from the ground state to the 5MC state, the metal to ligand bonds extend by unusually large values: by 0.29 angstrom in the axial and 0.21 angstrom in the equatorial direction. These results imply that the transition in the photochemical properties from typical Fe complexes to novel NHC compounds is manifested not only in the destabilization of the MC states, but also in structural distortion of these states.
Original languageEnglish
JournalChemical Science
Volume9
Issue number2
Pages (from-to)405-414
Number of pages10
ISSN2041-6520
DOIs
Publication statusPublished - 2018

Cite this

Leshchev, D., Harlang, T. C. B., Fredin, L. A., Khakhulin, D., Liu, Y., Biasin, E., ... Wulff, M. (2018). Tracking the picosecond deactivation dynamics of a photoexcited iron carbene complex by time-resolved X-ray scattering. Chemical Science, 9(2), 405-414. https://doi.org/10.1039/c7sc02815f
Leshchev, Denis ; Harlang, Tobias C. B. ; Fredin, Lisa A. ; Khakhulin, Dmitry ; Liu, Yizhu ; Biasin, Elisa ; Laursen, Mads G. ; Newby, Gemma E. ; Haldrup, Kristoffer ; Nielsen, Martin Meedom ; Warnmark, Kenneth ; Sundstrom, Villy ; Persson, Petter ; Kjær, Kasper Skov ; Wulff, Michael. / Tracking the picosecond deactivation dynamics of a photoexcited iron carbene complex by time-resolved X-ray scattering. In: Chemical Science. 2018 ; Vol. 9, No. 2. pp. 405-414.
@article{2ef0c0da4f154c3f9c9dbfe7e05ddc3f,
title = "Tracking the picosecond deactivation dynamics of a photoexcited iron carbene complex by time-resolved X-ray scattering",
abstract = "Recent years have seen the development of new iron-centered N-heterocyclic carbene (NHC) complexes for solar energy applications. Compared to typical ligand systems, the NHC ligands provide Fe complexes with longer-lived metal-to-ligand charge transfer (MLCT) states. This increased lifetime is ascribed to strong ligand field splitting provided by the NHC ligands that raises the energy levels of the metal centered (MC) states and therefore reduces the deactivation efficiency of MLCT states. Among currently known NHC systems, [Fe(btbip)2]2+ (btbip = 2,6-bis(3-tert-butyl-imidazol-1-ylidene)pyridine) is a unique complex as it exhibits a short-lived MC state with a lifetime on the scale of a few hundreds of picoseconds. Hence, this complex allows for a detailed investigation, using 100 ps X-ray pulses from a synchrotron, of strong ligand field effects on the intermediate MC state in an NHC complex. Here, we use time-resolved wide angle X-ray scattering (TRWAXS) aided by density functional theory (DFT) to investigate the molecular structure, energetics and lifetime of the high-energy MC state in the Fe-NHC complex  [Fe(btbip)2]2+ after excitation to the MLCT manifold. We identify it as a 260 ps metal-centered quintet (5MC) state, and we refine the molecular structure of the excited-state complex verifying the DFT results. Using information about the hydrodynamic state of the solvent, we also determine, for the first time, the energy of the 5MC state as 0.75 + 0.15 eV. Our results demonstrate that due to the increased ligand field strength caused by NHC ligands, upon transition from the ground state to the 5MC state, the metal to ligand bonds extend by unusually large values: by 0.29 angstrom in the axial and 0.21 angstrom in the equatorial direction. These results imply that the transition in the photochemical properties from typical Fe complexes to novel NHC compounds is manifested not only in the destabilization of the MC states, but also in structural distortion of these states.",
author = "Denis Leshchev and Harlang, {Tobias C. B.} and Fredin, {Lisa A.} and Dmitry Khakhulin and Yizhu Liu and Elisa Biasin and Laursen, {Mads G.} and Newby, {Gemma E.} and Kristoffer Haldrup and Nielsen, {Martin Meedom} and Kenneth Warnmark and Villy Sundstrom and Petter Persson and Kj{\ae}r, {Kasper Skov} and Michael Wulff",
year = "2018",
doi = "10.1039/c7sc02815f",
language = "English",
volume = "9",
pages = "405--414",
journal = "Chemical Science",
issn = "2041-6520",
publisher = "Royal Society of Chemistry",
number = "2",

}

Leshchev, D, Harlang, TCB, Fredin, LA, Khakhulin, D, Liu, Y, Biasin, E, Laursen, MG, Newby, GE, Haldrup, K, Nielsen, MM, Warnmark, K, Sundstrom, V, Persson, P, Kjær, KS & Wulff, M 2018, 'Tracking the picosecond deactivation dynamics of a photoexcited iron carbene complex by time-resolved X-ray scattering', Chemical Science, vol. 9, no. 2, pp. 405-414. https://doi.org/10.1039/c7sc02815f

Tracking the picosecond deactivation dynamics of a photoexcited iron carbene complex by time-resolved X-ray scattering. / Leshchev, Denis; Harlang, Tobias C. B.; Fredin, Lisa A.; Khakhulin, Dmitry; Liu, Yizhu; Biasin, Elisa; Laursen, Mads G.; Newby, Gemma E.; Haldrup, Kristoffer; Nielsen, Martin Meedom; Warnmark, Kenneth; Sundstrom, Villy; Persson, Petter; Kjær, Kasper Skov; Wulff, Michael.

In: Chemical Science, Vol. 9, No. 2, 2018, p. 405-414.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - Tracking the picosecond deactivation dynamics of a photoexcited iron carbene complex by time-resolved X-ray scattering

AU - Leshchev, Denis

AU - Harlang, Tobias C. B.

AU - Fredin, Lisa A.

AU - Khakhulin, Dmitry

AU - Liu, Yizhu

AU - Biasin, Elisa

AU - Laursen, Mads G.

AU - Newby, Gemma E.

AU - Haldrup, Kristoffer

AU - Nielsen, Martin Meedom

AU - Warnmark, Kenneth

AU - Sundstrom, Villy

AU - Persson, Petter

AU - Kjær, Kasper Skov

AU - Wulff, Michael

PY - 2018

Y1 - 2018

N2 - Recent years have seen the development of new iron-centered N-heterocyclic carbene (NHC) complexes for solar energy applications. Compared to typical ligand systems, the NHC ligands provide Fe complexes with longer-lived metal-to-ligand charge transfer (MLCT) states. This increased lifetime is ascribed to strong ligand field splitting provided by the NHC ligands that raises the energy levels of the metal centered (MC) states and therefore reduces the deactivation efficiency of MLCT states. Among currently known NHC systems, [Fe(btbip)2]2+ (btbip = 2,6-bis(3-tert-butyl-imidazol-1-ylidene)pyridine) is a unique complex as it exhibits a short-lived MC state with a lifetime on the scale of a few hundreds of picoseconds. Hence, this complex allows for a detailed investigation, using 100 ps X-ray pulses from a synchrotron, of strong ligand field effects on the intermediate MC state in an NHC complex. Here, we use time-resolved wide angle X-ray scattering (TRWAXS) aided by density functional theory (DFT) to investigate the molecular structure, energetics and lifetime of the high-energy MC state in the Fe-NHC complex  [Fe(btbip)2]2+ after excitation to the MLCT manifold. We identify it as a 260 ps metal-centered quintet (5MC) state, and we refine the molecular structure of the excited-state complex verifying the DFT results. Using information about the hydrodynamic state of the solvent, we also determine, for the first time, the energy of the 5MC state as 0.75 + 0.15 eV. Our results demonstrate that due to the increased ligand field strength caused by NHC ligands, upon transition from the ground state to the 5MC state, the metal to ligand bonds extend by unusually large values: by 0.29 angstrom in the axial and 0.21 angstrom in the equatorial direction. These results imply that the transition in the photochemical properties from typical Fe complexes to novel NHC compounds is manifested not only in the destabilization of the MC states, but also in structural distortion of these states.

AB - Recent years have seen the development of new iron-centered N-heterocyclic carbene (NHC) complexes for solar energy applications. Compared to typical ligand systems, the NHC ligands provide Fe complexes with longer-lived metal-to-ligand charge transfer (MLCT) states. This increased lifetime is ascribed to strong ligand field splitting provided by the NHC ligands that raises the energy levels of the metal centered (MC) states and therefore reduces the deactivation efficiency of MLCT states. Among currently known NHC systems, [Fe(btbip)2]2+ (btbip = 2,6-bis(3-tert-butyl-imidazol-1-ylidene)pyridine) is a unique complex as it exhibits a short-lived MC state with a lifetime on the scale of a few hundreds of picoseconds. Hence, this complex allows for a detailed investigation, using 100 ps X-ray pulses from a synchrotron, of strong ligand field effects on the intermediate MC state in an NHC complex. Here, we use time-resolved wide angle X-ray scattering (TRWAXS) aided by density functional theory (DFT) to investigate the molecular structure, energetics and lifetime of the high-energy MC state in the Fe-NHC complex  [Fe(btbip)2]2+ after excitation to the MLCT manifold. We identify it as a 260 ps metal-centered quintet (5MC) state, and we refine the molecular structure of the excited-state complex verifying the DFT results. Using information about the hydrodynamic state of the solvent, we also determine, for the first time, the energy of the 5MC state as 0.75 + 0.15 eV. Our results demonstrate that due to the increased ligand field strength caused by NHC ligands, upon transition from the ground state to the 5MC state, the metal to ligand bonds extend by unusually large values: by 0.29 angstrom in the axial and 0.21 angstrom in the equatorial direction. These results imply that the transition in the photochemical properties from typical Fe complexes to novel NHC compounds is manifested not only in the destabilization of the MC states, but also in structural distortion of these states.

U2 - 10.1039/c7sc02815f

DO - 10.1039/c7sc02815f

M3 - Journal article

VL - 9

SP - 405

EP - 414

JO - Chemical Science

JF - Chemical Science

SN - 2041-6520

IS - 2

ER -