Journal article
Detailed Characterization of a Nanosecond-Lived Excited State: X-ray and Theoretical Investigation of the Quintet State in Photoexcited [Fe(terpy)(2)](2+)
Hungarian Academy of Sciences1
Department of Chemistry, Technical University of Denmark2
Physical and Biophysical Chemistry, Department of Chemistry, Technical University of Denmark3
Department of Physics, Technical University of Denmark4
Neutrons and X-rays for Materials Physics, Department of Physics, Technical University of Denmark5
European Synchrotron Radiation Facility6
Argonne National Laboratory7
The Hamburg Centre for Ultrafast Imaging8
European XFEL9
Risø National Laboratory for Sustainable Energy, Technical University of Denmark10
Center for Atomic-scale Materials Design, Centers, Technical University of Denmark11
...and 1 moreTheoretical 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.
Language: | English |
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Publisher: | American Chemical Society |
Year: | 2015 |
Pages: | 5888-5902 |
ISSN: | 19327447 and 19327455 |
Types: | Journal article |
DOI: | 10.1021/acs.jpcc.5b00557 |
ORCIDs: | Haldrup, Kristoffer , Kjær, Kasper Skov , Dohn, Asmus Ougaard , Møller, Klaus Braagaard and Nielsen, Martin Meedom |