Syntheses, structures, photophysical properties and electroluminescent applications of dinuclear Copper(I) halide complexes containing 9-carbazolyl-substituted 1,2-Bis(diphenylphosphino)benzene

The studies on the photophysical properties of the copper(I) halide complexes based on rigid diphosphine ligands have attracted increasing attention. Here, six copper(I) halide complexes containing 9-carbazolyl-substituted 1,2-bis(diphenylphosphino)benzene, Cu₂X₂ (L1)₂ and Cu₂X₂ (L2)₂ [L1 = 1,2-bis(9-carbazolyl)-4,5-bis(diphenylphosphino)benzene, X = I (1), Br (2), Cl (3); L2 = 1-(9-carbazolyl)-3,4-bis(diphenylphosphino)benzene, X = I (4), Br (5), Cl (6)], were synthesized and characterized. In these complexes, two copper(I) centers are bridged by two halogen ligands to form a dinuclear structure with a four membered Cu₂X₂ ring. They exhibited efficient yellow green to yellowish orange delayed fluorescence in the powder state at ambient temperature, with peak wavelengths located between 548 and 602 nm (τ = 1.2–2.3 μs; Φ = 0.09–0.53). The introduction of one or two 9-carbazolyl substituents into the diphosphine resulted in the red shifting emission, shorter decay time and higher thermal stability of the complexes. The emission of the complexes originates from (metal + halide)-to-ligand and intraligand charge transitions. Organic light-emitting devices based on complex 1 exhibit yellow green luminescence with maximum external quantum efficiency of 12.0 % and current efficiency of 32.64 cd A⁻¹.