Near-Infrared Phosphorescent Silver Nanoclusters/Polyethylenimine Nanocomposites for Photothermal Conversion

Emerging as a promising functional material, metal nanoclusters that emit near-infrared (NIR) radiation have garnered significant attention due to their distinctive properties. Nonetheless, the rational design of NIR-emissive metal nanoclusters still faces substantial challenges. Herein, we demonstrate a self-assembly strategy for constructing NIR-emissive nanocomposites (abbreviated as Ag9-NCs/PEI) using water-soluble Ag9-NCs (Ag9(mba)9, where H2mba = 2-mercaptobenzoic acid) and branched polyethylenimine (PEI) (Mw = 750,000). The Ag9-NCs/PEI exhibits excellent phosphorescent properties, demonstrating a broad NIR phosphorescence band spanning from 750 to 1200 nm (NIR: >750 nm) and three-component microsecond lifetimes (τ1 = 2.22 μs; τ2 = 33.31 μs; τ3 = 230.76 μs) at room temperature. This behavior is attributed to the incorporation of three triplet emitting states, as verified by temperature-dependent steady/transient emission spectra and time-resolved transient emission spectra (TRES). More importantly, the Ag9-NCs/PEI nanocomposite also demonstrates exceptional photothermal conversion properties, with the temperature elevating promptly from 22 to 310 °C within just 10 s upon 660 nm laser irradiation (0.8 W/cm2). The notable phosphorescence, especially in the NIR region, is rarely observed in silver cluster nanocomposites.