Femtosecond M2,3-Edge Spectroscopy of Transition-Metal Oxides: Photoinduced Oxidation State Change in α-Fe2O3

Vura-Weis, Joshua; Jiang, Chang Ming; Liu, Chong; Gao, Hanwei; Lucas, J. Matthew; Groot, Frank M. F. de; Yang, Peidong; Alivisatos, A. Paul; Leone, Stephen R.

doi:10.1021/jz401997d

Cited by 126 publications

(175 citation statements)

References 35 publications

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“…Time-zero and the instrument response function of 105 fs FWHM were determined using concurrent transient absorption of α-Fe 2 O 3 , which displays IRF-limited formation of a ligand-to-metal charge transfer state. 23,24 Transient spectra at a range of pumpprobe delay times are shown in Figure 4A, with kinetic slices at selected energies in shown in Figure 4B. These spectra are analyzed using both single-energy kinetic fits and a global fit using a sequential These time constants are taken from the global fit (τ=1/k), and are summarized with fit uncertainties in Table 1.…”

Section: Transient M-edge Xanesmentioning

confidence: 99%

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Sub-100 fs Intersystem Crossing to a Metal-Centered Triplet in Ni(II)OEP Observed with M-Edge XANES

2019

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Nickel porphyrins have been extenstively studied as photosensitizers due to their long-lived metal-centered excited states. The multiplicity of the (d,d) state, and/or the rate of intersystem crossing between singlet and triplet metal-centered states, has remained uncertain due to the spin-insensitivity of many spectral probes. In this work, we directly probe the metal 3d shell occupation of nickel(II) octaethylporphyrin (NiOEP) using femtosecond M 2,3 -edge X-ray absorption near-edge structure (XANES). A tabletop high-harmonic source is used to perform 400 nm pump, extreme-ultraviolet probe transient absorption spectroscopy with ~100 fs time resolution. Photoexcitation produces a (π,π*) state that evolves with a time constant of 48 fs to a vibrationally hot metal-centered triplet 3 (d,d) excited state with a lifetime of 595 ps. The spin sensitivity of M-edge XANES allows the 3 (d,d) state to be distinguished from a potential 1 (d,d) state, as shown by charge transfer multiplet simulations and comparison to triplet nickel(II) oxide. Vibrational cooling of the hot triplet state occurs over tens of ps, with minimal change in the electronic structure of the nickel(II) center. No evidence of an LMCT or MLCT intermediate state is seen within the time resolution of the instrument, suggesting that if such a state exists in NiOEP it depopulates in <25 fs. Finally, this study demonstrates the ability of table highharmonic XUV sources to measure excited-state spin transitions in molecular transition metal complexes. 3

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Section: Transient M-edge Xanesmentioning

confidence: 99%

“…18 This technique has been used recently to resolve ultrafast photophysics of heme model complex iron(III)tetraphenylporphyrin chloride 19 as well as carrier photophysics in metal oxide semiconductors such as α-Fe 2 O 3 , Co 3 O 4 , and NiO. [20][21][22][23][24]…”

Section: Introductionmentioning

confidence: 99%

Sub-100 fs Intersystem Crossing to a Metal-Centered Triplet in Ni(II)OEP Observed with M-Edge XANES

2019

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“…Vura-Weis and collaborators [92], have remarkably demonstrated the power of high harmonic A c c e p t e d M a n u s c r i p t 16 …”

Section: Page 13 Of 23mentioning

confidence: 99%

Time resolved X-ray absorption spectroscopy in condensed matter: A road map to the future

Dell’Angela

Parmigiani

Malvestuto

2015

Journal of Electron Spectroscopy and Related Phenomena

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“…Because TRXL and TRXAS require X-ray pulses with high stability, high photon flux, and wide tenability (in case of TRXAS), most of time-resolved X-ray studies of solution-phase systems have been performed at third-generation synchrotron sources. However, table-top laser plasma sources, [175][176] which can achieve femtosecond temporal resolution, have also been used for time-resolved X-ray diffraction [177][178] and femtosecond XAS [179][180][181][182] experiments. Here we note that, in this review article, we focus on only our own research works performed using synchrotron sources rather than present a comprehensive …”

Section: Introductionmentioning

confidence: 99%

Tracking reaction dynamics in solution by pump–probe X-ray absorption spectroscopy and X-ray liquidography (solution scattering)

Kim

Oang

et al. 2016

Chem. Commun.

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Characterization of transient molecular structures formed during chemical and biological processes are essential for understanding their mechanisms and functions. Over the last decade, time-resolved X-ray liquidography (TRXL) and timeresolved X-ray absorption spectroscopy (TRXAS) have emerged as powerful techniques for molecular and electronic structural analysis of photoinduced reactions in solution phase. Both techniques make use of a pump-probe scheme that consists of (1) an optical pump pulse to initiate a photoinduced process and (2) an X-ray probe pulse to monitor changes in molecular structure as a function of time delay between pump and probe pulses. TRXL is sensitive to changes in global molecular structure and therefore can be used to elucidate structural changes of reacting solute molecules as well as the collective response of solvent molecules. On the other hand, TRXAS can be used to probe changes in both local geometrical and electronic structures of specific X-ray-absorbing atoms due to the element-specific nature of core-level transitions. These techniques are complementary to each other and a combination of the two methods will enhance the capability of accurately obtaining structural changes induced by photoexcitation. Here we review the principles of TRXL and TRXAS and present recent application examples of the two methods for studying chemical and biological processes in solution. Furthermore, we briefly discuss the prospect of using X-ray free electron lasers for the two techniques, which will allow us to keep track of structural dynamics on femtosecond time scales in various solution-phase molecular reactions.

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Femtosecond M_2,3-Edge Spectroscopy of Transition-Metal Oxides: Photoinduced Oxidation State Change in α-Fe₂O₃

Cited by 126 publications

References 35 publications

Sub-100 fs Intersystem Crossing to a Metal-Centered Triplet in Ni(II)OEP Observed with M-Edge XANES

Sub-100 fs Intersystem Crossing to a Metal-Centered Triplet in Ni(II)OEP Observed with M-Edge XANES

Time resolved X-ray absorption spectroscopy in condensed matter: A road map to the future

Tracking reaction dynamics in solution by pump–probe X-ray absorption spectroscopy and X-ray liquidography (solution scattering)

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