On the Near‐Infrared Photoluminescence and High‐Pressure Physical Chemistry of Gold Nanoclusters

ABSTRACT Gold nanoclusters have great potential as sensing and imaging materials for biomedical and biological applications, mainly owing to their intrinsic biocompatibility and their unique near‐infrared (NIR) active properties. Especially, the photoluminescence (PL) characteristics of gold nanoclusters, including the dual emission, large Stokes shift, long lifetime, the NIR‐II emission from ∼1000 to 1600 nm, and the thermally activated delayed fluorescence (TADF), distinguish the luminescent gold nanoclusters from other traditional emitters (e.g., organic dyes, quantum dots, and organometallic compounds). These intriguing PL characteristics mainly originate from the rich excited‐state structural and electronic behaviors of photoexcited gold nanoclusters. For a comprehensive understanding of the underlying PL mechanism of gold nanoclusters, a systematic spectroscopic study on structurally correlated series of atomically precise samples is required. The relatively low PL quantum yields have been a long‐time issue for gold nanoclusters, which are probably caused by their relatively slow radiative transition rates, and the rich excited‐state processes and non‐radiative pathways. Several recent studies show that the key to enhancing the PL of gold nanoclusters lies in the suppression of the non‐radiative decays and the removal of “redundant” excited‐state transitions. The recent high‐pressure studies provide an additional tool to modulate the structures and enhance the PL properties of metal nanoclusters beyond conventional synthetic chemistry.