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

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 H₂O, ∼60% in D₂O, 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 Au₃₈(pMBA)₂₄ to Au₇₆(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 Au₇₆(pMBA)₄₄. This photooxidation strategy opens a new pathway to the development of more highly emissive and photostable luminophores.