Luminescent Bimetallic Two-Coordinate Gold(I) Complexes Utilizing Janus Carbenes

A series of bimetallic carbene-metal-amide (cMa) complexes have been prepared with bridging biscarbene ligands to serve as a model for the design of luminescent materials with large oscillator strengths and small energy differences between the singlet and triplet states (ΔE_ST). The complexes have a general structure (R₂N)Au(:carbene─carbene:)Au(NR₂). The bimetallic complexes show solvation-dependent absorption and emission that is analyzed in detail. It is found that the molar absorptivity of the bimetallic complexes is correlated with the energy barrier to rotation of the metal-ligand bond. The bimetallic cMa complexes also exhibit short emission lifetimes (τ = 200-300 ns) with high photoluminescence efficiencies (Φ_PL > 95%). The radiative rates of bimetallic cMa complexes are 3-4 times faster than that of the corresponding monometallic complexes. Analysis of temperature-dependent luminescence data indicates that the lifetime for the singlet state (τ_S1) of bimetallic cMa complexes is near 12 ns with a ΔE_ST of 40-50 meV. The presented compounds provide a general design for cMa complexes to achieve small values for ΔE_ST while retaining high radiative rates. Solution-processed organic light-emitting devices (OLEDs) made using two of the complexes as luminescent dopants show high efficiency and low roll-off at high luminance.