Speaker
Description
The K edges of light elements reveal the crucial role of the ligands in mediating ultrafast decay cascades. In this talk, I will present our investigation of a prototypical spin crossover complex, iron II trisbipyridine. Upon optical excitation, the ensemble of molecules undergoes a cascade of relaxation processes starting from the singlet states, intersystem crossing to the triplet state, and finally relaxing to the quintet state, all within the first 400 fs [1,2,3]. The transition to the final quintet state is accompanied by a pronounced elongation of the Fe-N bond [1,2]. By probing the nitrogen 1s to π* resonance, we isolate the specific changes in the local environment of the coordinating nitrogen sites during this ultrafast cascade. In the figure, we present transient absorption spectra that reveal a prompt shift and delayed rise in the nitrogen absorption resonance, which is a signature of the intersystem crossing.
a) Transient absorption spectra over the first 0.8 ps; b) Experimental scheme used for self-referencing transmission measurements.
Beyond this specific case study, I will present the experimental setup available at the Maloja endstation and offered to users. TR-XAS in the transmission geometry for liquids is available in the energy range of 260 eV to 1000 eV, coupled with a wide variety of optical wavelengths. The liquid injector is based on the micro-chip design by Koralek et al [4], allowing tunable sheet thickness from several 10s of nanometers to microns.
References:
1- K. S. Kjær, Chemical Science 2019, 10, 5749.
2- B. E. Van Kuiken, The Journal of Physical Chemistry Letters 2016, 7, 465.
3- G. Auböck, M. Chergui, Nature Chemistry 2015, 7, 629.
4- Koralek et al. Nature Communications volume 9, 1353 (2018)
| Scientific Topics | Chemistry |
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