| 1. |
- Canton, Sophie, et al.
(författare)
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Toward Highlighting the Ultrafast Electron Transfer Dynamics at the Optically Dark Sites of Photocatalysts
- 2013
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 4:11, s. 1972-1976
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Tidskriftsartikel (refereegranskat)abstract
- Building a detailed understanding of the structure function relationship is a crucial step in the optimization of molecular photocatalysts employed in water splitting schemes. The optically dark nature of their active sites usually prevents a complete mapping of the photoinduced dynamics. In this work, transient X-ray absorption spectroscopy highlights the electronic and geometric changes that affect such a center in a bimetallic model complex. Upon selective excitation of the ruthenium chromophore, the cobalt moiety is reduced through intramolecular electron transfer and undergoes a spin flip accompanied by an average bond elongation of 0.20 +/- 0.03 angstrom. The analysis is supported by simulations based on density functional theory structures (B3LYP*/TZVP) and FEFF 9.0 multiple scattering calculations. More generally, these results exemplify the large potential of the technique for tracking elusive intermediates that impart unique functionalities in photochemical devices.
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| 2. |
- Vanko, Gyoergy, et al.
(författare)
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Detailed Characterization of a Nanosecond-Lived Excited State: X-ray and Theoretical Investigation of the Quintet State in Photoexcited [Fe(terpy)(2)](2+)
- 2015
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:11, s. 5888-5902
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical predictions show that depending on the populations of the Fe 3d(xy), 3d(xz), and 3d(yz) orbitals two possible quintet states can exist for the high-spin state of the photoswitchable model system [Fe(terpy)(2)](2+). The differences in the structure and molecular properties of these B-5(2) and E-5 quintets are very small and pose a substantial challenge for experiments to resolve them. Yet for a better understanding of the physics of this system, which can lead to the design of novel molecules with enhanced photoswitching performance, it is vital to determine which high-spin state is reached in the transitions that follow the light excitation. The quintet state can be prepared with a short laser pulse and can be studied with cutting-edge time-resolved X-ray techniques. Here we report on the application of an extended set of X-ray spectroscopy and scattering techniques applied to investigate the quintet state of [Fe(terpy)(2)](2+) 80 ps after light excitation. High-quality X-ray absorption, nonresonant emission, and resonant emission spectra as well as X-ray diffuse scattering data clearly reflect the formation of the high-spin state of the [Fe(terpy)(2)](2+) molecule; moreover, extended X-ray absorption fine structure spectroscopy resolves the Fe-ligand bond-length variations with unprecedented bond-length accuracy in time-resolved experiments. With ab initio calculations we determine why, in contrast to most related systems, one configurational mode is insufficient for the description of the low-spin (LS)-high-spin (HS) transition. We identify the electronic structure origin of the differences between the two possible quintet modes, and finally, we unambiguously identify the formed quintet state as 5E, in agreement with our theoretical expectations.
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| 3. |
- Vanko, Gyoergy, et al.
(författare)
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Spin-state studies with XES and RIXS: From static to ultrafast
- 2013
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048. ; 188, s. 166-171
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Tidskriftsartikel (refereegranskat)abstract
- We report on extending hard X-ray emission spectroscopy (XES) along with resonant inelastic X-ray scattering (RIXS) to study ultrafast phenomena in a pump-probe scheme at MHz repetition rates. The investigated systems include low-spin (LS) Fe-II complex compounds, where optical pulses induce a spin-state transition to their (sub)nanosecond-lived high-spin (HS) state. Time-resolved XES clearly reflects the spin-state variations with very high signal-to-noise ratio, in agreement with HS-LS difference spectra measured at thermal spin crossover, and reference HS-LS systems in static experiments, next to multiplet calculations. The 1s2p RIXS, measured at the Fe Is pre-edge region, shows variations after laser excitation, which are consistent with the formation of the HS state. Our results demonstrate that X-ray spectroscopy experiments with overall rather weak signals, such as RIXS, can now be reliably exploited to study chemical and physical transformations on ultrafast time scales. (C) 2012 Elsevier B.V. All rights reserved.
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