Synthesis of N-Heterocyclic Carbene Protected Gold Nanoclusters and their Applications in Electrocatalysis, Photodynamic Therapy and Bioimaging

Abstract

Gold nanoparticles (AuNPs) have demonstrated significant potential as radiosensitizers and photosensitizers. These unique materials have shown significant potential in electrocatalysis, therapeutics and bioimaging applications. Currently, the most widely investigated AuNPs are stabilized by thiols – a sulfur-bound ligand with limited stability and high oxidative vulnerability. This is problematic as it leaves the nanoparticles susceptible to degradation and corrosion during use, which limits their application. Furthermore, AuNPs consist of a mixture of particles with various sizes and ill-defined structures making structure-property relationships challenging to assess. Gold nanoclusters (AuNCs) are a subcategory of AuNPs that have well-defined structures, are monodisperse, and have unique and tuneable optical properties. Among AuNCs, those stabilized by N-heterocyclic carbenes (NHCs) – a carbon-bound ligand – are far more robust than their thiol-based counterparts and thus have high potential. In this work, we demonstrate how careful selection of ligand precursors and synthesis conditions allow access to various clusters and examine their structures and properties. We provide an in-depth investigation of three classes of nanoclusters (hydrido, ditopic, and heteroleptic) and demonstrate how different structures provide clusters with distinct applications. We demonstrate that NHC-protected clusters have valuable properties and are viable tools in the electrocatalytic reduction of CO2, the photodynamic destruction of cancer cells, and near-infrared bioimaging.