# Single-Atom Site Photocatalysts Boosting Organic Synthesis: The Integration of a Metal Active Site and Photosensitive Unit

## TL;DR

This paper explores how single-atom site catalysts improve photocatalytic organic synthesis by integrating metal active sites and photosensitive units.

## Contribution

The paper introduces the integration of metal active sites and photosensitive units in single-atom site catalysts to enhance photocatalytic efficiency.

## Key findings

- Single-atom site catalysts (SASCs) enable intramolecular electron transfer, boosting photocatalytic efficiency.
- SASCs anchored on semiconductor supports combine photosensitive units and metal sites into one system.
- Structure–activity relationships in SASCs are crucial for optimizing photocatalytic organic synthesis.

## Abstract

Metallaphotoredox catalysis merges the powerful bond-forming abilities of transition metal catalysis with unique electron or energy transfer pathways accessible in photoexcited states, injecting new vitality into organic synthesis. However, most transition metal catalysts cannot be excited by visible light. Thus, prevalent metallaphotoredox catalytic systems require dual catalysts: a transition metal catalyst and a separate photosensitizer. This leads to inefficient electron transfer between these two low-concentration catalytic species, which often limits overall photocatalytic performance. Single-atom site catalysts (SASCs) offer a promising solution, wherein isolated and quasi-homogeneous transition metal sites are anchored on heterogeneous supports. When semiconductors are employed as the support, the photosensitive unit and transition metal catalytic site can be integrated into one system. This integration switches the electron transfer mode from intermolecular to intramolecular, thereby significantly enhancing photocatalytic efficiency. Furthermore, such heterogeneous catalysts are easier to separate and reuse. This review summarizes recent advances in the application of SASCs for photocatalytic organic synthesis, with a particular focus on elucidating structure–activity relationships of the single-atom sites.