Mononuclear Cu(I) halide complexes containing asymmetric diphosphine and diphenyl pyridyl monophosphine: Structures and photophysical properties

Thermally activated delayed fluorescent (TADF) Cu(I) halide complexes have attracted attention due to their highly emission and short lifetimes (several mu s scale). Here, three mononuclear four-coordinate Cu(I) halide complexes containing asymmetric diphosphine and pyridyl phosphine, [CuX(L1)(L2)] (L1 = 2,3-bis(diphenylphoshino)thiophene, L2 = 2-(diphenylphosphino)pyridine, X = I (1), Br(2), Cl (3)), were synthesized and their structures and photophysical properties were characterized. At room temperature, complexes 1-3 in powder exhibit intense green to yellow green delayed fluorescence (lambda(em) = 497-523 nm, tau = 1.5-4.3 mu s, phi = 0.19-0.28). The emissions of the complexes 1-3 are originated from (metal + halide)-to-ligand and intra-ligand charge transfer. More contributions from MLCT and XLCT can result in the shorter decay lifetimes (1.6 similar to 4.3 mu s), which will prevent a roll-off of efficiency with increasing current density in OLED devices.