Synthesis, characterization and luminescent properties of copper(I) halide complexes containing biphenyl bidentate phosphine ligand

Copper(I) halide complexes having thermally activated delayed fluorescence (TADF) and phosphorescence have attracted much attention. Here, a series of four-coordinate dinuclear copper(I) halide complexes, [CuX(bpbp)]₂ (bpbp = 2,2′-bis(diphenylphosphino)biphenyl, X = I (1), Br (2) and Cl (3)), were synthesized, and their molecular structures and photophysical properties were investigated. The structural analysis reveals that two copper(I) centers are bridged by two halogen ligands to form a dinuclear structure with a four-membered Cu₂X₂ ring. These complexes exhibit yellow to blue emission in the solid state at room temperature and have peak emission wavelengths at 575–487 nm with microsecond lifetimes (τ = 6.2–19.8 μs) and low emission quantum yields (<0.01%). The emissions of 1–3 originate from MLCT, XLCT, and IL (intraligand) transitions. Three complexes displayed good thermal stability.