Identifying the triplet intermediate state in the ultrafast photoinduced spin-transition of low-spin iron(II) compounds using femtosecond m2,3-edge absorption spectroscopy

Zhang, Kaili

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https://hdl.handle.net/2142/104383 Copy

Description

Title

Identifying the triplet intermediate state in the ultrafast photoinduced spin-transition of low-spin iron(II) compounds using femtosecond m2,3-edge absorption spectroscopy

Author(s)

Zhang, Kaili

Contributor(s)

• Vura-Weis, Josh
• Girolami, Gregory S.
• de Groot, Frank
• Lin, Ming-Fu
• Verkamp, Max A.
• Benke, Kristopher
• Ryland, Elizabeth S.
• Ash, Ryan T.

Issue Date

2019-06-20

Keyword(s)

High-harmonic generation and XUV spectroscopy

Abstract

In this work, we perform femtosecond M$_{2,3}$-edge XANES on low-spin iron complexes using a high harmonic generation (HHG) light source. Low-spin iron complexes hold promise as affordable alternatives to ruthenium-based photosensitizers. Conventional iron complexes with polypyridyl ligands are unsuitable because the excitation energy is dissipated in 200 fs by ultrafast population of the low-lying quintet metastable state. This formally $\Delta$S=2 process is conjectured to proceed through a metal-centered triplet intermediate state, but spectroscopic evidence of such an intermediate has remained elusive. Here we use femtosecond M$_{2,3}$-edge XANES to elucidate the role of metal-centered intermediate states. The transient response of Fe(phen)$_{3}$(SCN)$_{2}$ following excitation in the MLCT band clearly shows the presence of a metal-centered $^{3}$T$_{1}$ state. The transient response also shows oscillations consistent with the evolution of a vibrational wave-packet on the quintet surface. We also recorded the M$_{2,3}$-edge transient response of Fe[(CF$_{3}$)$_{2}$bpca]$_{2}$, a complex with a weaker ligand field. A comparison of the photophysical behaviors of Fe(phen)$_{3}$(SCN)$_{2}$ and Fe[(CF$_{3}$)$_{2}$bpca]$_{2}$ sheds light on the influence of crystal field strength on the relaxation mechanism of the MLCT state. Our findings add a hitherto missing piece to the existing picture of photophysics of iron complexes.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/104383

DOI

https://doi.org/10.15278/isms.2019.RK03

Copyright and License Information

Copyright 2019 Kaili Zhang

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