Heteroleptic mononuclear Cu(i) halide complexes containing carbazolyl substituted phenyl diphosphine and monophosphine: structures and photophysical and electroluminescent properties

How to obtain heteroleptic mononuclear Cu(i) halide complexes with high quantum efficiency and short decay lifetime remains a challenge. Here, seven mononuclear four-coordinate Cu(i) halide complexes [CuX(DCzDP)(PPh₃)] (DCzDP = 1,2-bis(9-carbazolyl)-4,5-bis(diphenylphosphino)benzene, X = Br (1), Cl (2)), [CuX(DCzDP)(CzP)] (CzP = 9-methyl-3-(diphenylphosphino)carbazole, X = I (3), Br (4), Cl (5)) and [CuX(DCzDP)(DCzP)] (DCzP = bis(9-methyl-3-carbazolyl)phenylphosphine, X = I (6), Br (7)), were synthesized and their structures and photophysical properties were characterized. At room temperature, complexes 1-7 in the powder state emit a yellowish green to yellow green delayed fluorescence (λ_em = 531-560 nm, Φ = 0.34-0.75, τ = 1.8-2.9 μs). By replacing one phenyl group of PPh₃ with a 9-methyl-3-carbazolyl group, the PLQYs (photoluminescence quantum yields) of the complexes are effectively improved and the decay lifetimes are only around 2.0 μs. Among them, complex 4 displays the highest PLQY (0.75) and a short decay lifetime (1.9 μs). The radiative decay rate (k_r) is 3.95 × 10⁵ s⁻¹, which is the highest value among the reported heteroleptic mononuclear Cu(i) halide complexes and comparable with that of Ir(iii) complexes. Solution-processed organic light-emitting devices that contain complex 4 exhibit greenish yellow fluorescence with a maximum external quantum efficiency (EQE) of 6.56%