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

## TL;DR

Researchers improved the efficiency of iridium-based photocatalysts by using a proton-coupled electron transfer system inspired by natural processes.

## Contribution

A new iridium(III) complex with a BIP-Py group was developed to enable intramolecular multiproton-coupled electron transfer.

## Key findings

- The BIP-Py platform reduced charge recombination by ∼106-fold in photocatalytic reactions.
- Quantum yields increased by up to 157% with the new photocatalyst design.
- Infrared and visible spectroelectrochemistry confirmed protonation and charge-separated states via PCET.

## Abstract

In photoredox reactions,
charge recombination (CR) limits quantum
yields, hindering the efficient conversion of light energy into catalytic
activity. To address this, we drew inspiration from redox relays in
photosystem II (PSII) and developed a new series of iridium­(III) complexes
featuring covalently attached benzimidazole-phenol-pyridine (BIP-Py)
groups to facilitate intramolecular multiproton-coupled electron transfer
(MPCET). Herein, we evaluate the effects of MPCET through an extended
and well-defined hydrogen-bond network to improve photocatalytic activity
and mitigate rapid charge recombination. Infrared spectroelectrochemistry
reveals pyridine protonation upon phenol oxidation, while visible
spectroelectrochemistry and transient absorption spectroscopy confirm
the electro- and photochemical formation of charge-separated states
(CSS) involving oxidized BIP, resulting from intramolecular proton-coupled
electron transfer (PCET). The application of the BIP-Py platform in
a photocatalytic N-hydroxyphthalimide ester reduction
reaction resulted in a ∼106-fold reduction in CR rate and a
quantum yield enhancement of up to 157%. Our findings suggest that
incorporating MPCET-based redox relays into photocatalyst frameworks
is an effective strategy to enhance the efficiency of photocatalytic
systems.