Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 141, Issue 43, Pages 17180-17188Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.9b07332
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Funding
- National Science Foundation [1555245]
- Air Force Office of Scientific Research [FA9550-14-1-0314]
- William and Janet Lycan Fund at the University of Illinois
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [1555245] Funding Source: National Science Foundation
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Fe(II) coordination complexes are promising alternatives to Ru(II) and Ir(III) chromophores for photoredox chemistry and solar energy conversion, but rapid deactivation of the initial metal-to-ligand charge transfer (MLCT) state to low-lying (d,d) states limits their performance. Relaxation to a long-lived quintet state is postulated to occur via a metal-centered triplet state, but this mechanism remains controversial. We use femtosecond extreme ultraviolet (XUV) transient absorption spectroscopy to measure the excited-state relaxation of Fe(phen)(3)(2+) and conclusively identify a T-3 intermediate that forms in 170 fs and decays to a vibrationally hot T-5(2g) state in 39 fs. A coherent vibrational wavepacket with a period of 249 fs and damping time of 0.63 ps is observed on the T-5(2g) surface, and the spectrum of this oscillation serves as a fingerprint for the Fe-N symmetric stretch. The results show that the shape of the M-2,M-3-edge X-ray absorption near-edge structure (XANES) spectrum is sensitive to the electronic structure of the metal center, and the high-spin sensitivity, fast time resolution, and tabletop convenience of XUV transient absorption make it a powerful tool for studying the complex photophysics of transition metal complexes.
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