Highly Efficient Copper(I) Emitters Supported by Secondary Metal‐Ligand Interactions

Abstract The most prominent way of tuning optoelectronic properties of copper(I) emitters is primary‐sphere ligand engineering, but little attention is placed on noncovalent interactions. Here, an effective strategy is demonstrated to introduce secondary metal‐ligand interactions into two‐coordinate Cu(I) emitters with the goals of optimizing conformations and improving optical properties. As a proof of concept, a panel of Cu(I) complexes is developed via chalcogen‐heterocyclic engineering on the 1,2‐positions of carbazole ligand. The S‐embedded complexes have distinct noncovalent metal‐ligand interactions originating from S···Cu orbital contacts, verified by single‐crystal structure and theoretical simulation. Thanks to the flattened conformations stabilized by secondary metal‐ligand interactions, the optimized Cu(I) emitters afford high emission quantum yields of up to 93% and short radiative lifetimes of down to 0.8 µs. Cu‐12BT and Cu‐12BF support the resultant organic light‐emitting diodes (OLEDs) delivering outstanding maximum external quantum efficiencies (EQEs) of 24.3% and 28.6%, respectively, among the best performance for Cu(I) emitters. The optimal devices based on Cu‐12BF also achieve 18.7% EQE at the practical luminance of 100 nits. This work unlocks the large potential of noncovalent interactions in developing excellent Cu(I) emitters for cost‐effective and high‐efficiency OLEDs.