Harnessing of Cooperative Cu⋅⋅⋅H Interactions for Luminescent Low-Coordinate Copper(I) Complexes towards Stable OLEDs

Although two-coordinate Cu(I) complexes are highly promising low-cost emitters for organic light-emitting diodes (OLEDs), the exposed metal center in the linear coordination geometry makes them suffer from poor stability. Herein, we describe a strategy to develop stable carbene-Cu-amide complexes through installing intramolecular noncovalent Cu⋅⋅⋅H interactions. The employment of 13H-dibenzo[a,i]carbazole (DBC) as the amide ligand leads to short Cu⋅⋅⋅H distances in addition to the Cu-N coordination bond. The resultant Cu(I) complexes exhibit yellow thermally activated delayed fluorescence with photoluminescence quantum yields of up to 86 % and radiative decay rate constants on the order of 10⁶ s^-1. Comparing with the analogues without Cu⋅⋅⋅H interactions, the pincer complexes have significantly improved stability. The vacuum-deposited OLEDs show high-performance electroluminescence with maximum external quantum efficiencies of up to 29.5 % and extremely small roll-offs of only 3.5 % at 10,000 cd m^-2. Remarkably, the operational lifetimes (LT₉₀) are up to 68 h with an initial luminance of 3000 cd m^-2. This work proves a feasible design of robust low-coordinate metal complexes by leveraging secondary coordination interactions, which helps to overcome the long-standing stability problem.