Thermally Activated Delayed Fluorescence-Based Near-Infrared-II Luminescence and Controlled Size Growth of Silver Nanoclusters

Due to the significant relationships between structure and properties, the controlled construction of atomically precise metal clusters presents both a formidable challenge and great importance. The innovative synthesis of well-defined silver nanoclusters with near-infrared II (NIR-II) luminescent properties may inspire further exploration of functional metal nanoclusters for bioimaging applications. In this study, we employed the multidentate chelating nitrogen ligand 3,5-di(2-pyridyl)pyrazole (Hbpypz) to construct three unprecedented silver nanoclusters: [Ag₂₇(bpypz)₁₄]³⁺ (<b>Ag</b>_<b>27</b>), [Ag₆₂(bpypz)₁₈]⁶⁺ (<b>Ag</b>_<b>62</b>), and [Ag₉₁(bpypz)₂₄]⁵⁺ (<b>Ag</b>_<b>91</b>). Single-crystal X-ray analysis indicated that these cluster structures stem from Ag₁₃ units, exhibiting cluster-of-cluster configurations. By modulating the stoichiometry of the chelating ligand and silver centers, we achieved controlled size growth and reversible cluster-to-cluster conversions among these silver nanoclusters. Notably, the <b>Ag</b>_<b>27</b> nanocluster exhibits an interesting thermally activated delayed fluorescence (TADF) based luminescence in the second near-infrared (NIR-II) region and demonstrates high catalytic efficiency in the oxidative coupling of benzylamines via a singlet oxygen (¹O₂) oxidation mechanism.