Leveraging Intramolecular π-Stacking to Access an Exceptionally Long-Lived 3MC Excited State in an Fe(II) Carbene
Robert J Ortiz1, Rajarshi Mondal1, James K McCusker2
1Department of Chemistry and the Manitoba Institute for Materials, University of Manitoba, 144 Dysart Road, Winnipeg, Manitoba R3T 2N2, Canada.
Journal of the American Chemical Society
|January 6, 2025
Summary
Researchers developed a novel iron complex with a significantly extended triplet metal-centered (3MC) excited-state lifetime of 4.1 ns. This breakthrough in molecular design stabilizes excited states for potential applications in photosensitizers and chromophores.
Area of Science:
- Photochemistry
- Inorganic Chemistry
- Materials Science
Background:
- Molecular structure manipulation is key for abundant-metal photosensitizers.
- Long-lived excited states are crucial for efficient photochemistry.
- Triplet metal-centered (3MC) excited states are vital for photoactivity but historically short-lived in Fe(II) complexes.
Purpose of the Study:
- To design and synthesize an Fe(II) complex with a stabilized, long-lived triplet metal-centered (3MC) excited state.
- To investigate the factors contributing to the stabilization of the 3MC excited state.
- To achieve excited-state lifetimes orders of magnitude longer than previously observed for Fe(II) complexes.
Main Methods:
- Synthesis of a novel Fe(II) coordination complex featuring strong-field donors and intramolecular π-stacking.
- Variable-temperature time-resolved absorption spectroscopy.
- Analysis using theoretical models (Arrhenius, Marcus theory) and computational modeling.
- X-ray crystallography for structural determination.
Main Results:
- A stable triplet metal-centered (3MC) excited state with a lifetime of 4.1 ± 0.3 ns was achieved in fluid solution at room temperature.
- Strong-field donors and intramolecular π-stacking were identified as key stabilizing factors.
- A Jahn-Teller stabilized excited state with a high activation barrier for ground-state recovery was revealed.
- The observed 3MC excited-state lifetime is orders of magnitude longer than in any previously reported Fe(II) complex.
Conclusions:
- Molecular design, specifically incorporating strong-field donors and π-stacking, can effectively stabilize long-lived triplet metal-centered (3MC) excited states in Fe(II) complexes.
- This stabilization is attributed to a Jahn-Teller effect and a high barrier to ground-state recovery.
- The achieved long-lived 3MC excited state opens new avenues for Fe(II) complexes in photochemistry and related applications.
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