Synthesis, Structures, Photophysics, and Electroluminescence of Dinuclear Carbene-Au(I)-Amide Complexes Featuring the...

Two-coordinate carbene-metal-amide (CMA) complexes have shown rich photophysical properties endowed by their tunable electronic structures and flexible conformations, which can be exploited for optoelectronic applications. Different from most of the studies on mononuclear CMA complexes, we herein report a series of dinuclear CMA-type gold(I) complexes, namely 1a, 1b, 2a, and 2b, using 1,1'-bicarbazole as a bridging donor ligand. Single-crystal X-ray structures reveal different conformations in terms of the torsion angles between the carbene and amide ligands that are affected by the steric effect of the carbene ligands. Close intramolecular face-to-face π-π contacts between the carbene and amide ligand planes are observed for 1a and 1b, featuring a twisted conformation. Complexes 1a and 2a containing pyrazine-fused N-heterocyclic carbenes (NHCs) exhibit thermally activated delayed fluorescence with photoluminescence quantum yields of 0.85 and 0.27 and short lifetimes of 408 and 289 ns in doped films. Theoretical calculations suggest mixed through-bond charge transfer and through-space charge transfer character for the emitting state. Vacuum-deposited organic light-emitting devices using 1a as the emitting dopant show a maximum external quantum efficiency of 20.5% and negligible roll-off at 1000 cd m^-2. This study demonstrates that the luminescent properties of CMA complexes can be further tuned by increasing the structural diversity.