X-ray absorption spectroscopy of exemplary platinum porphyrin and corrole derivatives: metal- <i>versus</i> ligand-centered oxidation

2022

J. Phys. Chem. A

Femtosecond X-ray absorption spectroscopy at the Ir O3-edge and N6,7-edges is performed on the photocatalyst iridium(III) tris(2-phenylpyridine), Ir(III)(ppy)3 using a tabletop high-harmonic source. Extreme ultraviolet (XUV) absorption between 44 and 76 eV measures transitions from the Ir 5p 3/2 and 4f 5/2,7/2 core to 5d valence orbitals, and the position of these spectral features is shown to be sensitive to the oxidation state and ligand field of the metal center. Upon excitation of the singlet metal-to-ligand charge transfer (1MLCT) band at 400 nm, a shift in the spectra due to the formation of the Ir(IV) center is observed, as is the creation of a new spectral feature corresponding to transitions into the t2g hole. Vibrational cooling of the MLCT state on the 3 and 16 ps time scales is measured as changes in the intensity of the transient features. This work establishes XUV spectroscopy as a useful tool for measuring the electronic structure of third row transition metal photosensitizers and catalysts at ultrafast time scales.

Section: ■ Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Femtosecond Extreme Ultraviolet Spectroscopy of an Iridium Photocatalyst Reveals Oxidation State and Ligand Field Specific Dynamics

2022

J. Phys. Chem. A

“…Similar shifts based on ligand field strengths have also been noted at the L 2,3 -edges for 3rd row metals; a recent example with platinum macrocyclic compounds showed that exchanging weaker field ligands (porphyrin, chloride) for stronger field ligands (corrole, pyridine, alkyl) in octahedral Pt(IV) compounds resulted in a 0.4 eV blue shift of the Pt L 3 -edge. 50 This shift was caused by the corresponding rise in the dorbital manifold due to the strengthened ligand interactions. While the shift observed in this work between the iridium(III) species is larger (2 eV vs 0.4 eV), this can be attributed to the more dramatic ligand field strength difference of six chloride ligands versus three bidentate 2phenylpyridine ligands.…”

Section: Resultsmentioning

confidence: 99%

Femtosecond extreme ultraviolet spectroscopy of an iridium photocatalyst reveals oxidation state and ligand field specific dynamics

2022

Preprint

Femtosecond X-ray absorption spectroscopy at the Ir O3-edge and N6,7-edges is performed on the photocatalyst iridium(III) tris(2-phenylpyridine), Ir(III)(ppy)3 using a tabletop high-harmonic source. Extreme ultraviolet (XUV) absorption between 44 eV and 72 eV measures transitions from the Ir 5p3/2 and 4f5/2,7/2 core to 5d valence orbitals, and the position of these spectral features is shown to be sensitive to the oxidation state and ligand field of the metal center. Upon excitation of the singlet metal-to-ligand charge transfer (1MLCT) band at 400 nm, a shift in the spectra due to the formation of the Ir(IV) center is observed, as is the creation of a new spectral feature corresponding to transitions into the t2g hole. Vibrational cooling of the MLCT state on the 3 ps and 16 ps timescales is measured as changes in the intensity of the transient features. This work establishes XUV spectroscopy as a useful tool for measuring the electronic structure of 3rd row transition metal photosensitizers and catalysts at ultrafast timescales.

“…Similar shifts based on ligand field strengths have also been noted at the L 2,3 -edges for 3rd row metals; a recent example with platinum macrocyclic compounds showed that exchanging weaker field ligands (porphyrin, chloride) for stronger field ligands (corrole, pyridine, alkyl) in octahedral Pt(IV) compounds resulted in a 0.4 eV blue shift of the Pt L 3 -edge. 51 This shift was caused by the corresponding rise in the dorbital manifold due to the strengthened ligand interactions. While the shift observed in this work between the iridium(III) species is larger (2 eV vs 0.4 eV), this can be attributed to the more dramatic ligand field strength difference of six chloride ligands versus three bidentate 2phenylpyridine ligands.…”

Section: Resultsmentioning

confidence: 99%

Femtosecond extreme ultraviolet spectroscopy of an iridium photocatalyst reveals oxidation state and ligand field specific dynamics

2022

Preprint

Femtosecond X-ray absorption spectroscopy at the Ir O3-edge and N6,7-edges is performed on the photocatalyst iridium(III) tris(2-phenylpyridine), Ir(III)(ppy)3 using a tabletop high-harmonic source. Extreme ultraviolet (XUV) absorption between 44 eV and 72 eV measures transitions from the Ir 5p3/2 and 4f5/2,7/2 core to 5d valence orbitals, and the position of these spectral features is shown to be sensitive to the oxidation state and ligand field of the metal center. Upon excitation of the singlet metal-to-ligand charge transfer (1MLCT) band at 400 nm, a shift in the spectra due to the formation of the Ir(IV) center is observed, as is the creation of a new spectral feature corresponding to transitions into the t2g hole. Vibrational cooling of the MLCT state on the 3 ps and 16 ps timescales is measured as changes in the intensity of the transient features. This work establishes XUV spectroscopy as a useful tool for measuring the electronic structure of 3rd row transition metal photosensitizers and catalysts at ultrafast timescales.