Photooxidation‐Induced Ultrabright and Ultraphotostable NIR‐II Emissive Water‐Soluble Gold Nanoclusters

Abstract The long‐standing issues of photobleaching and low photoluminescence quantum yield (QY) in the second near‐infrared (NIR‐II) region greatly hinder the luminophore's downstream applications. Herein we developed an ingenious method of continuous light illumination to achieve water‐soluble gold nanoclusters with both ultra‐high QY in NIR‐II region (∼14% in H 2 O, ∼60% in D 2 O, the highest QY among NIR‐II emitting water‐soluble nanoclusters with typical QY<1%) and ultra‐high photostability where emission remained completely unchanged under several hours’ illumination. Photooxidation‐induced transformation of Au 38 (pMBA) 24 to Au 76 (pMBA) 44 (pMBA = 4‐mercaptobenzoic acid) has been demonstrated to be the mechanism of the emission enhancement. The accelerated inter‐system crossing rate, extended lowest triplet lifetime, and suppressed nonradiative decay collectively contribute to the higher QY of Au 76 (pMBA) 44 . This photooxidation strategy opens a new pathway to the development of more highly emissive and photostable luminophores.