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 CH 3 CN ( Ag 4 ), CH 3 OH [ Ag 4 (CH 3 OH) 2 ], C 2 H 5 OH [ Ag 4 (C 2 H 5 OH) ], and i ‐C 3 H 7 OH [ Ag 2 ( i ‐C 3 H 7 OH) 2 ] realizing near‐unity FRET efficiency. Among them, Ag 4 (CH 3 OH) 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 Ag 4 , 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.