Understanding the NIR Emission of Metal Nanoclusters Through a Ligand-Shell-Kernel Triad Picture.

Near-infrared (NIR)-emitting noble metal nanoclusters have received significant research interest due to their low toxicity and feasible tunability, yet their practical applications remain constrained because of low photoluminescence quantum yields (PLQYs). Although ligand engineering and structural modulation strategies have advanced, the synergistic interplay among ligands, shells, and kernels in governing luminescence mechanisms remains poorly understood. Here, we elucidate the structural determinants of emission efficiency by comparing the photophysics of two quasi-isomeric PtAg nanoclusters stabilized by adamantanethiol (HS-Adm) and triphenylphosphine (PPh) (denoted as PtAg-1) and cyclohexanethiol (HS-CH) and PPh (denoted as PtAg-2). A 1.8-fold enhancement in PLQY for PtAg-1 (4.9%) relative to PtAg-2 (2.7%) was observed. This improvement arises from the synergistic effects of rigid adamantanethiol ligands (in PtAg-1), which suppress high-frequency vibrational modes, the geometric stability of the face-centered cubic (FCC) kernel, and reduced electron-vibration coupling, collectively reducing nonradiative relaxation. By establishing a ligand-shell-kernel triad framework, we demonstrate that rigid ligands minimize nonradiative decay, structural rigidity suppresses electron-vibration coupling in the shell, and a compact kernel facilitates blue-shifted emission. This multidimensional model transcends conventional approaches focused on isolated structural factors, offering a rational design principle for engineering high-performance nanocluster emitters with tailored PLQYs.