Second‐Sphere Coordination Boosted Afterglow Performance of Luminescent Copper(I) Complexes for Anti‐Counterfeiting Applications

The development of copper(I) complexes with long‐lived emission remains a significant challenge, as their intrinsic metal‐to‐ligand charge transfer or cluster‐centered triplet states typically restrict lifetimes to the microsecond range. Herein, a cyclic trinuclear copper(I) complex, Cu 3 (L1) 3 ( 1 , where HL1 = 9‐(5‐(3,5‐dimethyl‐1H‐pyrazol‐4‐yl)pyridine‐2‐yl)‐9H‐carbazole), is reported exhibiting exceptional yellow afterglow at room temperature. While the ligand HL1 exhibit weak orange afterglow with an average lifetime of 374.77 ms, complex 1 display yellow afterglow with a remarkable lifetime of 474.03 ms, the longest reported for single‐component Cu(I) complexes. Structural and theoretical analyses revealed that intermolecular Cu···N interactions in 1 create a rigid supramolecular framework. This framework suppresses nonradiative decay by stabilizing triplet excitons and enhances spin‐orbit coupling via Cu‐to‐pyridine charge transfer. Control experiments with a non‐Cu···N analog Cu 3 (L2) 3 ( 2 ) confirmed this mechanism, as 2 exhibited only 43.94 ms afterglow. Notably, 1 demonstrated reversible photoluminescence switching under O 2 , thermal, solvent, and mechanical stimuli, a rare multistimuli‐responsive behavior in Cu(I) complexes, underscoring its potential for advanced anti‐counterfeiting applications. This work not only introduces a unique multistimuli‐responsive afterglow material but also provides a second‐sphere coordination strategy to enhance afterglow performance in Cu(I)‐based emitters.