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Detailed Characterization of a Nanosecond-Lived Excited State: X-ray and Theoretical Investigation of the Quintet State in Photoexcited $[Fe(terpy)_{2}]^{2+}$
EuXFEL staff, Other
Author group:
Instrument FXE
Theoretical predictions show that depending on the populations of the $Fe$ $3_{dxy}$, $3_{dxz}$, and $3_{dyz}$ 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 $^{5}B_{2}$ and $^{5}E$ 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 $^{5}E$, in agreement with our theoretical expectations.
Washington, DC, Soc., 2015
Journal Information:
J. Phys. Chem. C, 119, 11, 5888-5902 (2015)
Related external records:
DOI: 10.1021/acs.jpcc.5b00557
WOS: WOS:000351557800015


 Record created 2016-10-11, last modified 2019-02-12

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