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Updated: Jun 27, 2025
12:19
Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization
Published on: November 29, 2018
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Intra- and Intermolecular Charge-Transfer Dynamics of Carbene-Metal-Amide Photosensitizers
Michael S Kellogg1, Austin R Mencke1, Collin N Muniz1
1Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States.
Summary
This study characterizes carbene-metal-amide (cMa) complexes used as photosensitizers. Researchers detailed excited-state kinetics, intersystem crossing, and charge transfer, revealing structure-property relationships for improved catalytic applications.
Area of Science:
- Photochemistry and Photophysics
- Organometallic Chemistry
- Catalysis
Background:
- Carbene-metal-amide (cMa) complexes are vital photosensitizers in electrocatalysis.
- Understanding excited-state dynamics is crucial for optimizing photosensitizer efficiency.
Purpose of the Study:
- To comprehensively characterize the excited-state kinetics and photophysical properties of eight cMa complexes (M = Cu, Au).
- To elucidate the relationship between molecular structure and photophysical behavior in these photosensitizers.
Main Methods:
- Utilized steady-state and time-resolved spectroscopies, including picosecond-to-nanosecond (psTA) and nanosecond-to-millisecond (nsTA) transient absorption spectroscopy.
- Employed time-correlated single photon counting (TCSPC) and a thermally activated delayed fluorescence (TADF) model.
- Conducted pulse radiolysis and bulk electrolysis experiments.
Main Results:
- Characterized excited-state kinetics, intersystem crossing (ISC) rates (∼3-120 × 10^9 s^-1), and energy gaps (ΔE_ST, 73-115 meV), showing systematic variations with molecular structure.
- Observed early-time relaxation (∼0.2-0.8 × 10^12 s^-1) attributed to solvent relaxation and vibrational cooling.
- Demonstrated efficient intermolecular charge transfer in a gold-based cMa complex and identified excited states as ligand-ligand charge transfer.
Conclusions:
- The study provides a detailed understanding of the photophysical processes governing cMa photosensitizers.
- Systematic structural modifications influence ISC rates and excited-state properties, offering pathways for rational design.
- The findings are critical for advancing photosensitized electrocatalytic reactions.
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