TY  - JOUR
A1  - Eckert, Sebastian
A1  - Mascarenhas, Eric Johnn
A1  - Mitzner, Rolf
A1  - Jay, Raphael Martin
A1  - Pietzsch, Annette
A1  - Fondell, Mattis
A1  - Vaz da Cruz, Vinicius
A1  - Föhlisch, Alexander
T1  - From the free ligand to the transition metal complex
BT  - FeEDTA(-) formation seen at ligand K-Edges
JF  - Inorganic chemistry
N2  - Chelating agents are an integral part of transition metal complex chemistry with broad biological and industrial relevance. The hexadentate chelating agent ethylenediaminetetraacetic acid (EDTA) has the capability to bind to metal ions at its two nitrogen and four of its carboxylate oxygen sites. We use resonant inelastic X-ray scattering at the 1s absorption edge of the aforementioned elements in EDTA and the iron(III)-EDTA complex to investigate the impact of the metal-ligand bond formation on the electronic structure of EDTA. Frontier orbital distortions, occupation changes, and energy shifts through metal- ligand bond formation are probed through distinct spectroscopic signatures.
KW  - Energy
KW  - Ligands
KW  - Metals
KW  - Nitrogen
KW  - Oxygen
Y1  - 2022
U6  - https://doi.org/10.1021/acs.inorgchem.2c00789
SN  - 0020-1669
SN  - 1520-510X
VL  - 61
IS  - 27
SP  - 10321
EP  - 10328
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Eckert, Sebastian
A1  - Niskanen, Johannes
A1  - Jay, Raphael Martin
A1  - Miedema, Piter S.
A1  - Fondell, Mattis
A1  - Kennedy, Brian
A1  - Quevedo, Wilson
A1  - Iannuzzi, Marcella
A1  - Föhlisch, Alexander
T1  - Valence orbitals and local bond dynamics around N atoms of histidine under X-ray irradiation
JF  - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2  - The valence orbitals of aqueous histidine under basic, neutral and acidic conditions and their X-ray induced transformations have been monitored through N 1s resonant inelastic X-ray scattering. Using density functional ab initio molecular dynamics simulations in the core-hole state within the Z + 1 approximation, core-excitation-induced molecular transformations are quantified. Spectroscopic evidence for a highly directional X-ray-induced local N-H dissociation within the scattering duration is presented for acidic histidine. Our report demonstrates a protonation-state and chemical-environment dependent propensity for a molecular dissociation, which is induced by the absorption of high energy photons. This case study indicates that structural deformations in biomolecules under exposure to ionizing radiation, yielding possible alteration or loss of function, is highly dependent on the physiological state of the molecule upon irradiation.
Y1  - 2017
U6  - https://doi.org/10.1039/c7cp05713j
SN  - 1463-9076
SN  - 1463-9084
VL  - 19
SP  - 32091
EP  - 32098
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Eckert, Sebastian
A1  - Norell, Jesper
A1  - Jay, Raphael Martin
A1  - Fondell, Mattis
A1  - Mitzner, Rolf
A1  - Odelius, Michael
A1  - Föhlisch, Alexander
T1  - T-1 Population as the Driver of Excited-State Proton-Transfer in 2-Thiopyridone
JF  - Chemistry - a European journal
N2  - Excited-state proton transfer (ESPT) is a fundamental process in biomolecular photochemistry, but its underlying mediators often evade direct observation. We identify a distinct pathway for ESPT in aqueous 2-thiopyridone, by employing transient N1s X-ray absorption spectroscopy and multi-configurational spectrum simulations. Photoexcitations to the singlet S-2 and S-4 states both relax promptly through intersystem crossing to the triplet T-1 state. The T-1 state, through its rapid population and near nanosecond lifetime, mediates nitrogen site deprotonation by ESPT in a secondary intersystem crossing to the S-0 potential energy surface. This conclusively establishes a dominant ESPT pathway for the system in aqueous solution, which is also compatible with previous measurements in acetonitrile. Thereby, the hitherto open questions of the pathway for ESPT in the compound, including its possible dependence on excitation wavelength and choice of solvent, are resolved.
KW  - excited-state proton-transfer
KW  - intersystem crossing
KW  - nitrogen
KW  - photochemistry
KW  - X-ray absorption
Y1  - 2019
U6  - https://doi.org/10.1002/chem.201804166
SN  - 0947-6539
SN  - 1521-3765
VL  - 25
IS  - 7
SP  - 1733
EP  - 1739
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - GEN
A1  - Fondell, Mattis
A1  - Eckert, Sebastian
A1  - Jay, Raphael Martin
A1  - Weniger, Christian
A1  - Quevedo, Wilson
A1  - Niskanen, Johannes
A1  - Kennedy, Brian
A1  - Sorgenfrei, Florian
A1  - Schick, Daniel
A1  - Giangrisostomi, Erika
A1  - Ovsyannikov, Ruslan
A1  - Adamczyk, Katrin
A1  - Huse, Nils
A1  - Wernet, Philippe
A1  - Mitzner, Rolf
A1  - Föhlisch, Alexander
T1  - Time-resolved soft X-ray absorption spectroscopy in transmission mode on liquids at MHz repetition rates
T2  - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe
N2  - We present a setup combining a liquid flatjet sample delivery and a MHz laser system for time-resolved soft X-ray absorption measurements of liquid samples at the high brilliance undulator beamline UE52-SGM at Bessy II yielding unprecedented statistics in this spectral range. We demonstrate that the efficient detection of transient absorption changes in transmission mode enables the identification of photoexcited species in dilute samples. With iron(II)-trisbipyridine in aqueous solution as a benchmark system, we present absorption measurements at various edges in the soft X-ray regime. In combination with the wavelength tunability of the laser system, the set-up opens up opportunities to study the photochemistry of many systems at low concentrations, relevant to materials sciences, chemistry, and biology.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 780 
KW  - l-edge xas
KW  - electronic-structure
KW  - molecular-structure
KW  - spin-state
KW  - dynamics
KW  - complexes
KW  - probe
KW  - water
KW  - iron(II)
KW  - spectra
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-437529
SN  - 1866-8372
IS  - 780
ER  - 
TY  - JOUR
A1  - Fondell, Mattis
A1  - Eckert, Sebastian
A1  - Jay, Raphael Martin
A1  - Weniger, Christian
A1  - Quevedo, Wilson
A1  - Niskanen, Johannes
A1  - Kennedy, Brian
A1  - Sorgenfrei, Florian
A1  - Schick, Daniel
A1  - Giangrisostomi, Erika
A1  - Ovsyannikov, Ruslan
A1  - Adamczyk, Katrin
A1  - Huse, Nils
A1  - Wernet, Philippe
A1  - Mitzner, Rolf
A1  - Föhlisch, Alexander
T1  - Time-resolved soft X-ray absorption spectroscopy in transmission mode on liquids at MHz repetition rates
JF  - Structural dynamics
N2  - We present a setup combining a liquid flatjet sample delivery and a MHz laser system for time-resolved soft X-ray absorption measurements of liquid samples at the high brilliance undulator beamline UE52-SGM at Bessy II yielding unprecedented statistics in this spectral range. We demonstrate that the efficient detection of transient absorption changes in transmission mode enables the identification of photoexcited species in dilute samples. With iron(II)-trisbipyridine in aqueous solution as a benchmark system, we present absorption measurements at various edges in the soft X-ray regime. In combination with the wavelength tunability of the laser system, the set-up opens up opportunities to study the photochemistry of many systems at low concentrations, relevant to materials sciences, chemistry, and biology. (C) 2017 Author(s).
Y1  - 2017
U6  - https://doi.org/10.1063/1.4993755
SN  - 2329-7778
VL  - 4
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - THES
A1  - Jay, Raphael Martin
T1  - Principles of charge distribution and separation
BT  - the case of iron complexes probed by X-ray spectroscopy
N2  - The electronic charge distributions of transition metal complexes fundamentally determine their chemical reactivity. Experimental access to the local valence electronic structure is therefore crucial in order to determine how frontier orbitals are delocalized between different atomic sites and electronic charge is spread throughout the transition metal complex. To that end, X-ray spectroscopies are employed in this thesis to study a series of solution-phase iron complexes with respect to the response of their local electronic charge distributions to different external influences. Using resonant inelastic X-ray scattering (RIXS) and X-ray absorption spectroscopy (XAS) at the iron L-edge, changes in local charge densities are investigated at the iron center depending on different ligand cages as well as solvent environments. A varying degree of charge delocalization from the metal center onto the ligands is observed, which is governed by the capabilities of the ligands to accept charge density into their unoccupied orbitals. Specific solvents are furthermore shown to amplify this process. Solvent molecules of strong Lewis-acids withdraw charge from the ligand allowing in turn for more metal charge to be delocalized onto the ligand. The resulting local charge deficiencies at the metal center are, however, counteracted by competing electron-donation channels from the ligand towards the iron, which are additionally revealed. This is interpreted as a compensating effect which strives to maintain local charge densities at the iron center. This mechanism of charge density preservation is found to be of general nature. Using time-resolved RIXS and XAS at the iron L-edge, an analogous interplay of electron donation and back-donation channels is also revealed for the case of charge-transfer excited states. In such transient configurations, the electronic occupation of iron-centered frontier orbitals has been altered by an optical excitation. Changes in local charge densities that are expected to follow an increased or decreased population of iron-centered orbitals are, however, again counteracted. By scaling the degree of electron donation from the ligand onto the metal, local charge densities at the iron center can be efficiently maintained. Since charge-transfer excitations, however, often constitute the initial step in many electron transfer processes, these findings challenge common notions of charge-separation in transition metal dyes.
KW  - L-edge spectroscopy
KW  - charge-transfer excitations
KW  - transition metal complexes
KW  - electronic structure
KW  - photo-chemical pathways
Y1  - 2020
ER  - 
TY  - JOUR
A1  - Jay, Raphael Martin
A1  - Eckert, Sebastian
A1  - Fondell, Mattis
A1  - Miedema, Piter S.
A1  - Norell, Jesper
A1  - Pietzsch, Annette
A1  - Quevedo, Wilson
A1  - Niskanen, Johannes
A1  - Kunnus, Kristjan
A1  - Föhlisch, Alexander
T1  - The nature of frontier orbitals under systematic ligand exchange in (pseudo-)octahedral Fe(II) complexes
JF  - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2  - Understanding and controlling properties of transition metal complexes is a crucial step towards tailoring materials for sustainable energy applications. In a systematic approach, we use resonant inelastic X-ray scattering to study the influence of ligand substitution on the valence electronic structure around an aqueous iron(II) center. Exchanging cyanide with 2-2′-bipyridine ligands reshapes frontier orbitals in a way that reduces metal 3d charge delocalization onto the ligands. This net decrease of metal–ligand covalency results in lower metal-centered excited state energies in agreement with previously reported excited state dynamics. Furthermore, traces of solvent-effects were found indicating a varying interaction strength of the solvent with ligands of different character. Our results demonstrate how ligand exchange can be exploited to shape frontier orbitals of transition metal complexes in solution-phase chemistry; insights upon which future efforts can built when tailoring the functionality of photoactive systems for light-harvesting applications.
Y1  - 2018
U6  - https://doi.org/10.1039/c8cp04341h
SN  - 1463-9076
SN  - 1463-9084
VL  - 20
IS  - 44
SP  - 27745
EP  - 27751
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Jay, Raphael Martin
A1  - Eckert, Sebastian
A1  - Vaz da Cruz, Vinicius
A1  - Fondell, Mattis
A1  - Mitzner, Rolf
A1  - Föhlisch, Alexander
T1  - Covalency-driven preservation of local charge densities in a metal-to-ligand charge-transfer excited iron photosensitizer
JF  - Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition
N2  - Charge-density rearrangements after metal-to-ligand charge-transfer excitation in an iron photosensitizer are investigated by R. M Jay, A. Fohlisch et al. in their Communication (DOI: 10.1002/anie.201904761). By using time-resolved X-ray absorption spectroscopy, surprising covalency-effects are revealed that inhibit charge-separation at the intra-molecular level. Furthermore, the underlying mechanism is proposed to be generally in effect for all commonly used photosensitizers in light-harvesting applications, which challenges the common perception of electronic charge-transfer.
KW  - charge-transfer
KW  - density functional calculations
KW  - iron
KW  - photochemistry
KW  - X-ray absorption spectroscopy
Y1  - 2019
U6  - https://doi.org/10.1002/anie.201904761
SN  - 1433-7851
SN  - 1521-3773
VL  - 58
IS  - 31
SP  - 10742
EP  - 10746
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Kühn, Danilo
A1  - Giangrisostomi, Erika
A1  - Jay, Raphael Martin
A1  - Sorgenfrei, Florian
A1  - Föhlisch, Alexander
T1  - The influence of x-ray pulse length on space-charge effects in optical pump/x-ray probe photoemission
JF  - New journal of physics : the open-access journal for physics
N2  - Pump-probe photoelectron spectroscopy (PES) is a versatile tool to investigate the dynamics of transient states of excited matter. Vacuum space-charge effects can mask these dynamics and complicate the interpretation of electron spectra. Here we report on space-charge effects in Au 4f photoemission from a polycrystalline gold surface, excited with moderately intense 90 ps (FWHM) soft x-ray probe pulses, under the influence of the Coulomb forces exerted by a pump electron cloud, which was produced by intense 40 fs laser pulses. The experimentally observed kinetic energy shift and spectral broadening of the Au 4f lines, measured with highly-efficient time-of-flight spectroscopy, are in good agreement with simulations utilizing a mean-field model of the electrostatic pump electron potential. This confirms that the line broadening is predominantly caused by variations in the take-off time of the probe electrons without appreciable influence of local scattering events. Our findings might be of general interest for pump-probe PES with picosecond-pulse-length sources.
KW  - space-charge effects
KW  - mean-field model
KW  - x-ray photoemission
KW  - electron spectroscopy
KW  - pump-probe
KW  - ARTOF
Y1  - 2019
U6  - https://doi.org/10.1088/1367-2630/ab2f5c
SN  - 1367-2630
VL  - 21
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Kühn, Danilo
A1  - Müller, Moritz
A1  - Sorgenfrei, Florian
A1  - Giangrisostomi, Erika
A1  - Jay, Raphael Martin
A1  - Ovsyannikov, Ruslan
A1  - Martensson, Nils
A1  - Sanchez-Portal, Daniel
A1  - Föhlisch, Alexander
T1  - Directional sub-femtosecond charge transfer dynamics and the dimensionality of 1T-TaS2
JF  - Scientific reports
N2  - For the layered transition metal dichalcogenide 1T-TaS2, we establish through a unique experimental approach and density functional theory, how ultrafast charge transfer in 1T-TaS2 takes on isotropic three-dimensional character or anisotropic two-dimensional character, depending on the commensurability of the charge density wave phases of 1T-TaS2. The X-ray spectroscopic core-hole-clock method prepares selectively in-and out-of-plane polarized sulfur 3p orbital occupation with respect to the 1T-TaS2 planes and monitors sub-femtosecond wave packet delocalization. Despite being a prototypical two-dimensional material, isotropic three-dimensional charge transfer is found in the commensurate charge density wave phase (CCDW), indicating strong coupling between layers. In contrast, anisotropic two-dimensional charge transfer occurs for the nearly commensurate phase (NCDW). In direct comparison, theory shows that interlayer interaction in the CCDW phase - not layer stacking variations - causes isotropic three-dimensional charge transfer. This is presumably a general mechanism for phase transitions and tailored properties of dichalcogenides with charge density waves.
Y1  - 2019
U6  - https://doi.org/10.1038/s41598-018-36637-0
SN  - 2045-2322
VL  - 9
IS  - 488
PB  - Nature Publ. Group
CY  - London
ER  -