Mechanistic exploration and controlled synthesis of precise thiolate-gold nanoclusters

Abstract

Well-defined thiolate-gold nanoclusters (generally described as Aun(SR)m NCs, where “n” and “m” are the numbers of gold atoms and thiolate ligands (–SR), respectively), comprise a family of ultrasmall particles (<2nm), which are distinctly different from their large counterparts, plasmonic gold nanoparticles (NPs, >2nm). They are attracting increasing attention in various areas, including biomedicine, optoelectronics, catalysis, and analytical science, mainly because of their unique molecular-like properties, such as HOMO-LUMO (highest occupied and lowest unoccupied molecular orbital) transitions, quantized charging, and photoluminescence. All of these physicochemical properties are highly sensitive to the size and composition of Au NCs, and thus the ability to control these variables during synthesis is highly important. This review describes recent advances in the precise control of these features during Au NC synthesis, typically via the reduction of Au(I)-SR complexes. First, the formation mechanisms for atomically precise Aun(SR)m NCs are explained, which may be decoupled into two stages: 1) generation of intermediate NCs via the reduction of Au(I)-SR complexes (reduction-assisted growth stage), and 2) size evolution of intermediate NCs to form Au NC species with atomic precision (size evolution stage). The size/composition control strategies implemented in the reduction-assisted growth stage are summarized based on this reduction-size evolution mechanism. Details are then given of the regulation strategies with effects in the size evolution stage. Finally, it is shown that balancing the rate of reduction and size evolution may be a unified approach for the facile synthesis (large-scale production, easy preparation, and short reaction time) of Aun(SR)m NCs with high control over their size and composition. This concept may facilitate the design and development of large-scale methods for synthesizing stable well-defined Au NCs with advanced functions for use in a wide range of applications in different domains.