A Hydrogen Bond-Mediated Förster Resonance Energy Transfer (FRET) Glue Strategy for Long-Lived Room-Temperature Phosphorescence From Silver Clusters.

Luminescent coinage metal clusters (CMCs) hold great promise for bioimaging and optical applications, but long-lived room-temperature phosphorescence (RTP) with high quantum yield remains challenging. Herein, a Förster resonance energy transfer (FRET) glue strategy using Ag+ to bridge donor-acceptor (D/A) pairs is adopted to synthesize a series of clusters in CH3CN (Ag4), CH3OH [Ag4(CH3OH)2], C2H5OH [Ag4(C2H5OH)], and i-C3H7OH [Ag2(i-C3H7OH)2] realizing near-unity FRET efficiency. Among them, Ag4(CH3OH)2 delivers superior thermally activated delayed phosphorescence with a high photoluminescence quantum yield of 96% and an ultralong RTP lifetime of around 100 ms, which are 5.6 times and 400 times higher than those of Ag4, respectively. Mechanistic studies reveal that isolated Ag+ as single-point linkers circumvent the overly strong spin-orbit coupling of larger Ag cores while retaining an appropriate heavy-atom effect to facilitate effective phosphorescence emission. In addition, hydrogen bonds from coordinating solvents can adjust the spatial position of ligand, optimizing D/A arrangement, which enhances FRET efficiency and suppresses nonradiative deactivation, ultimately achieving high-efficiency luminescence of silver clusters. Leveraging the solvent-mediated regulation of cluster structure and performance, this system enables reversible single-crystal-to-single-crystal transformation and subsequent time-solvent-temperature-gated multilevel information encryption. This work provides a general design principle for CMCs with high-performance RTP.