Abstract: Gold nanoclusters (Au NCs) feature atomically precise structures with core sizes ranging from 1 to 3 nm, serving as a unique system that bridges organometallic molecules and conventional gold nanoparticles; combining molecular-like properties with the advantages of nanomaterials, their transition from a molecular state to a metallic state is one of the core issues in the field of nanoscience. As large-sized gold nanoclusters (containing >100 gold atoms) increase in size, their energy levels gradually shift from discrete to continuous, exhibiting metallic properties. However, this transition is not solely determined by size, and a critical size regime exists. Within this critical size regime, the clusters exhibit dual molecular and metallic properties, which are synergistically regulated by multiple factors including crystal structure and geometric morphology, and this phenomenon has been extensively and intensively investigated. This review summarizes the research progress on the metallicity evolution of large-sized gold nanoclusters, outlines the structure-activity relationships among size, structure, and metallicity for non-metallic, metallic, and critical-regime clusters, and clarifies the determination criteria and key research techniques for metallicity. Finally, the future challenges and development directions in this field are discussed.

Key words: Gold nanoclusters, Metallicity, Size evolution, Femtosecond transient absorption spectroscopy