Formation of Multiple Emission Centers of Gold Nanoclusters during the Aggregation-Induced Emission Process

The controversy over the emission center of metal nanoclusters (MNCs) has been going on for decades. A question important for understanding the photoluminescence mechanisms of metal clusters is whether a single cluster can contain several independent photoluminescent emitters. Herein, using the widely studied aggregation-induced emission and a ligand-exchange strategy, gold nanoclusters (Au NCs) with multiple emission peaks (∼460, ∼560, and ∼620 nm) are synthesized. The photoluminescence is excitation wavelength independent and is from supramolecular clusters formed by the assembly of functional groups on the nanoconfined surface of an individual Au NC. Water clusters confined in the hydrophobic nanocavity can also act as an emission center of Au NCs. P-band states formed by the overlapping of p-orbitals from heteroatoms (O, N, S, and P) of adjacent functional groups dominate the energy level structure of MNCs and thus the photoluminescence properties.