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Pursuing Heteroleptic Ligand Design Principles for Photoactive Fe Complexes with Ultrafast X-ray Emission and
Hyeongtaek Lim1, Karl C Nielsen2, Natalia E Powers-Riggs1
1Stanford PULSE Institute, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California94025, United States.
Journal of the American Chemical Society
|August 12, 2026
Summary
Investigating iron complexes using X-ray emission spectroscopy reveals how ligand structure affects excited state lifetimes. This guides the design of better photosensitizers for photocatalysis.
Area of Science:
- Photochemistry and Photophysics
- Inorganic Chemistry
- Materials Science
Background:
- Understanding transition metal complexes is crucial for developing efficient photosensitizers.
- Time-resolved X-ray emission spectroscopy (XES) is effective for studying electronic excited states.
Purpose of the Study:
- To investigate the excited state dynamics of a heteroleptic Fe(II) polypyridyl carbene complex.
- To understand how ligand structure influences photophysical properties and excited state relaxation.
Main Methods:
- Time-resolved Fe Kβ X-ray emission spectroscopy (XES).
- Variable-temperature transient optical absorption (VT-TA) spectroscopy.
- Density functional theory (DFT) calculations and Eyring analysis.
Main Results:
- Identified parallel excited state relaxation dynamics, assigning the long-lived state to a triplet metal-centered state.
- DFT calculations showed that ligand structural flexibility and arrangement significantly impact excited state relaxation.
- Ligand arrangement affects the energy of Jahn-Teller active triplet metal-centered states in low-spin d6 metal complexes.
Conclusions:
- Constraining ligand flexibility with multidentate ligands enhances excited state lifetimes.
- Ligand design principles can be developed to extend metal-to-ligand charge transfer excited state lifetimes in heteroleptic Fe complexes.
- This research provides insights for designing improved photosensitizers for photocatalysis.
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