Leveraging Multiproton-Coupled Electron Transfer to Improve Ir(III) Photocatalyst Efficiency

Area of Science:

• Photocatalysis
• Organometallic Chemistry
• Energy Conversion

Background:

• Charge recombination (CR) in photoredox reactions limits quantum yields and hinders efficient light energy conversion.
• Inspiration drawn from redox relays in Photosystem II (PSII) to overcome CR limitations.
• Development of advanced photocatalyst designs is crucial for efficient solar energy applications.

Purpose of the Study:

• To design and synthesize novel iridium(III) complexes with covalently attached benzimidazole-phenol-pyridine (BIP-Py) groups.
• To investigate the role of intramolecular multiproton-coupled electron transfer (MPCET) in enhancing photocatalytic activity.
• To mitigate rapid charge recombination (CR) by utilizing an extended hydrogen-bond network.

Main Methods:

• Synthesis of iridium(III) complexes featuring BIP-Py moieties.
• Infrared spectroelectrochemistry to monitor pyridine protonation.
• Visible spectroelectrochemistry and transient absorption spectroscopy to study charge-separated states (CSS).

Main Results:

• Evidence of pyridine protonation upon phenol oxidation and formation of CSS via intramolecular proton-coupled electron transfer (PCET).
• Demonstrated a ~106-fold reduction in CR rate in a photocatalytic N-hydroxyphthalimide ester reduction.
• Achieved up to a 157% enhancement in quantum yield using the BIP-Py photocatalyst platform.

Conclusions:

• MPCET-based redox relays integrated into photocatalyst frameworks effectively enhance photocatalytic efficiency.
• The BIP-Py platform offers a promising strategy for designing next-generation photocatalysts.
• This work provides a new avenue for improving light energy conversion in catalytic systems.