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Dirhodium(II,II) Complexes as Panchromatic Single-Molecule Photocatalysts for Hydrogen Evolution
1Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43214, United States.
Accounts of Chemical Research
|June 2, 2025
Summary
This study introduces robust, air-stable rhodium-based single-molecule photocatalysts for efficient hydrogen production. These catalysts exhibit broad light absorption and high turnover frequencies, offering a promising sustainable energy solution.
Area of Science:
- Photocatalysis
- Sustainable Energy
- Coordination Chemistry
Background:
- Growing global energy demand and climate change necessitate a shift to sustainable energy sources.
- Hydrogen production via solar energy is an attractive sustainable energy strategy.
- Single-molecule photocatalysts offer advantages over multicomponent systems by integrating light absorption and catalysis.
Purpose of the Study:
- To investigate the photophysical properties and catalytic mechanisms of novel rhodium-based single-molecule photocatalysts for hydrogen evolution.
- To assess the stability, light absorption range, and efficiency of these photocatalysts.
- To elucidate the reaction pathways involved in photocatalytic proton reduction.
Main Methods:
- Synthesis and characterization of rhodium-dimer complexes with benzo[c]cinnoline ligands.
- Ground and excited-state photophysical measurements, including absorption, emission, and lifetime studies.
- Theoretical calculations (DFT) to assign molecular orbitals and understand electronic transitions.
- Electrochemical and photocatalytic experiments to determine reaction mechanisms and efficiency.
Main Results:
- Developed robust, air-stable single-molecule photocatalysts with panchromatic absorption from UV to NIR.
- Achieved high turnover frequencies (20–30 h⁻¹) under red light irradiation.
- Identified the lowest-energy absorption as a singlet metal/ligand-to-ligand charge transfer (¹ML-LCT) transition.
- Determined excited-state reduction potential of ~+1.0 V vs Ag/AgCl, indicating strong oxidizing ability.
- Established that hydrogen evolution occurs via sequential photon absorption and reduction events, generating Rh₂(II,II) species, with the benzo[c]cinnoline ligand acting as the active site.
Conclusions:
- Rh₂(II,II) complexes represent highly efficient single-molecule photocatalysts for hydrogen evolution, overcoming limitations of previous systems.
- The detailed mechanistic insights provide a foundation for designing improved photocatalysts.
- This work paves the way for developing similar catalysts using earth-abundant metals.
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