Electrochemiluminescence Monitoring of the Ligand Exchange Process of Gold Nanoclusters

Ligand exchange reaction (LER) plays an important role in the synthesis and postmodification of metal nanoclusters (MNCs). However, due to the challenges in the analysis of the metal-ligand interface, the approaches of revealing the ligand exchange process of MNCs still lag behind. In this work, a detailed ligand exchange process of MNCs was revealed by monitoring their electrochemiluminescence (ECL) signals. Taking tetrakis(hydroxymethyl) phosphonium chloride (THPC)-gold nanoclusters (AuNCs) as a model for the existing nanocluster and 8-mercaptooctanoic acid (MOA) as a model for the incoming ligand, the ECL intensities of THPC/MOA-AuNCs first increased and then decreased before ultimately reaching a stable plateau. Further investigation confirmed that the initial increase in ECL corresponded to ligand replacement on the surface of AuNCs, while the subsequent ECL decrease was attributed to ligand rearrangement. Both the ligand replacement and ligand shell reconstruction processes modulated interligand interactions and ligand-to-metal charge transfer (LMCT) properties, thereby altering the electronic band of AuNCs and ultimately tuning their ECL emission performances. The developed ECL-based approach for monitoring LER also exhibited universal applicability, which can successfully extend to the other AuNCs with different ligand pairs. This work not only provides deep insight into the correlation between the ECL intensity and surface dynamics of MNCs but also offers a convenient approach to monitor the ligand exchange process of MNCs.