Promoted Photocatalytic Hydrogen Evolution by Tuning the Electronic State of Copper Sites in Metal-Organic Supramolecular Assemblies

The electronic state in terms of charge and spin of metal sites is fundamental to govern the catalytic activity of a photocatalyst. Herein, we show that modulation of the electronic states of Cu sites, without changing the coordination environments, of two metal-organic supramolecular assemblies based on pi & sdot;& sdot;& sdot;pi stacking can significantly improve photocatalytic activity. The use of these heterogeneous photocatalysts, without using noble metal cocatalysts, resulted in an increase of the hydrogen production rate from 522 to 3620 mu mol h-1 g-1. A systematical analysis revealed that the charge density and spin density of the metal centers are efficiently modulated via the modulation of the coordination fields around active copper (II) centers by the variation of the non-coordination groups of terminal ligands, leading to the significant enhancement of photocatalytic activity. This work provides an insight into the electronic state of active metal centers for designing high-performance photocatalysts. Two metal-organic supramolecular assemblies based on pi & sdot;& sdot;& sdot;pi stacking were synthesized as heterogeneous noble-metal-free photocatalysts for hydrogen evolution. Without changing the coordination environments or the supramolecular structures, the spin and charge density of the Cu sites were tuned by modulating terminal ligands, resulting in an increased rate of photocatalytic hydrogen production.image

Automated summary

In this study, the modulation of electronic states of metal centers was shown to significantly improve the photocatalytic activity of the catalyst. By tuning the coordination fields around active copper (II) centers through the modulation of terminal ligands, the charge density and spin density of the metal centers were efficiently controlled, leading to enhanced photocatalytic activity. This work provides insights into the design of high-performance photocatalysts by understanding the electronic state of active metal centers.