Photoluminescence of ligand-protected gold nanoclusters: progress in experimental and theoretical studies.

Ligand-protected gold nanoclusters, with their small sizes and atomically precise structures, exhibit unique photophysical properties that position them as promising candidates for applications in bioimaging, sensing, and optoelectronics. However, except for a few ligand-protected gold nanoclusters, their photoluminescence quantum yield (PLQY) is still relatively low, and the underlying emission mechanisms are not yet fully elucidated. This review highlights recent experimental and theoretical advances aimed at enhancing and elucidating the photoluminescence (PL) mechanisms of ligand-protected gold nanoclusters. Experimentally, strategies such as heterometallic doping, ligand engineering, and structural rigidification have been employed to promote radiative transitions and suppress nonradiative decay, resulting in substantial improvements in PLQY. Theoretically, methods including density functional theory (DFT), time-dependent density functional theory (TDDFT), and nonadiabatic molecular dynamics (NA-MD) have provided important insights into the PL origin, emission pathways, and excited-state dynamics of ligand-protected gold nanoclusters. These advances will deepen our understanding of structure-property relationships in ligand-protected gold nanoclusters and pave the way for the rational design of highly emissive gold nanoclusters.