Highly efficient blue–green neutral dinuclear copper(I) halide complexes containing bidentate phosphine ligands

Recently, copper(I) complexes having thermally activated delayed fluorescence (TADF) have attracted much attention. Here, a series of new neutral luminescent dinuclear copper(I) halide complexes with the chelating ligand, 1,2-bis(diphenylphosphino)-4,5-dimethylbenzene (dpmb) were synthesized, and their molecular structures and photophysical properties were investigated. They consist of halogen-bridged dinuclear structures, [Cu(μ-X)dpmb]₂ (X=I (1), Br (2), Cl (3)). In the solid state, these complexes display intense blue–green photoluminescence with lifetimes in the microsecond regime (λ_max=498–527 nm; Φ=0.28–0.32; τ=2.5–12.5 μs) at 298 K. The emission of the complexes originate from the (σ+X)→π^* transition, where σ is the σ bond between Cu and P and X is the halogen. The organic light-emitting devices (OLEDs) using complexes 1–3 as the dopant emitters exhibit bright green luminescence with current efficiencies of 32.9 cd A⁻¹ and maximum external quantum efficiencies of 10.1%.