| 1. |
- Canton, Sophie, et al.
(author)
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Probing the Anisotropic Distortion of Photoexcited Spin Crossover Complexes with Picosecond X-ray Absorption Spectroscopy
- 2014
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In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:8, s. 4536-4545
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Journal article (peer-reviewed)abstract
- For numerous spin crossover complexes, the anisotropic distortion of the first coordination shell around the transition metal center governs the dynamics of the high-spin/low-spin interconversion. However, this structural parameter remains elusive for samples that cannot be investigated with crystallography. The present work demonstrates how picosecond X-ray absorption spectroscopy is able to capture this specific deformation in the photoinduced high-spin state of solvated [Fe(terpy)(2)](2+), a complex which belongs to the prominent family of spin crossover building blocks with nonequivalent metal-ligand bonds. The correlated changes in Fe-N-Axial, Fe-N-Distal, and bite angle N-Distal-Fe-N-Axial extracted from the measurements are in very good agreement with those predicted by DFT calculations in D-2d symmetry. The outlined methodology is generally applicable to the characterization of ultrafast nuclear rearrangements around metal centers in photoactive molecular complexes and nanomaterials, including those that do not display long-range order.
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| 2. |
- Zhang, Xiaoyi, et al.
(author)
-
Highly Accurate Excited-State Structure of [Os(bpy)(2)dcbpy](2+) Determined by X-ray Transient Absorption Spectroscopy
- 2014
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 136:24, s. 8804-8809
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Journal article (peer-reviewed)abstract
- Determining the electronic and geometric structures of photoexcited transient species with high accuracy is crucial for understanding their fundamental photochemistry and controlling their photoreactivity. We have applied X-ray transient absorption spectroscopy to measure the XANES and EXAFS spectra of a dilute (submillimolar) solution of the osmium(II) polypyridyl complex [Os(bpy)(2)dcbpy](PF6)(2) (dcbpy = 4,4'-dicarboxy-2,2'-bipyridine) (OsL2L') in methanol at the Os L-III edge. We have obtained spectra of superb quality for both the ground state and the photoinduced (MLCT)-M-3 excited state that have allowed us not only to extract detailed information about the Os 5d orbitals but also to resolve very small differences of 0.010 +/- 0.008 angstrom in the average Os-N bond lengths of the ground and excited states. Theoretical calculations using a recently developed DFT-based approach support the measured electronic structures and further identify the nature of the molecular orbitals that contribute to the main absorption bands in the XANES spectra.
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| 3. |
- Zhang, Xiaoyi, et al.
(author)
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Visualizing Interfacial Charge Transfer in Ru-Dye-Sensitized TiO2 Nanoparticles Using X-ray Transient Absorption Spectroscopy
- 2011
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In: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 2:6, s. 628-632
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Journal article (peer-reviewed)abstract
- A molecular level understanding of the structural reorganization accompanying interfacial electron transfer is important for rational design of solar cells. Here we have applied XTA (X-ray transient absorption) spectroscopy to study transient structures in a heterogeneous interfacial system mimicking the charge separation process in dye-sensitized solar cell (DSSC) with Ru(dcbpy)(2)(NCS)(2) (RuN3) dye adsorbed to TiO2 nanopartide surfaces. The results show that the average Ru-NCS bond length reduces by 0.06 angstrom, whereas the average Ru-N(dcbpy) bond length remains nearly unchanged after the electron injection. The differences in bond-order change and steric hindrance between two types of ligands are attributed to their structural response in the charge separation. This study extends the application of XTA into optically opaque hybrid interfacial systems relevant to the solar energy conversion.
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