Multicolor reversible fluorescence of cellulosic gold nanoclusters via pH-triggered ligand recombination

Understanding pH-triggered the correlation between ligand competitive recombination and fluorescence color in di-ligand gold nanoclusters (AuNCs) is crucial for achieving on-demand programming of multicolor fluorescence. Here, pH-responsive cellulosic di-ligand AuNCs with multicolor fluorescence switching were developed by realizing cysteine and glutathione ligand exchange on gold cores. The di-ligand AuNCs were stabilized onto cellulose nanocrystals and possessed ultra-long fluorescence stability (around 1.5 years). The cysteine and glutathione ligands on the auric nucleus of the cellulosic di-ligand AuNCs demonstrated pH-induced reversible dynamic competition. When the environment changed from alkaline to neutral or acidic, glutathione emerged as the dominant ligand instead of cysteine, resulting in reversible dynamic recombination in AuNCs. Accordingly, the AuNCs exhibited smooth and reversible pH-induced fluorescence switching from green to blue to red at pH values of 8-13, 5-7, and 2-4, respectively, following 365 nm UV excitation. These pH-triggered di-ligand AuNCs were successfully demonstrated to have potential applications in dynamic anti-counterfeiting authentication and multicolor dynamic information encryption. This study provides a new strategy for designing novel multicolor AuNCs promoting their applicability and important insights for understanding the dynamic reconstruction process of di-ligand AuNCs triggered by pH.