Synthesis And Properties Study Of Copper (Ⅰ) Complexes With New Benzimidazolylphosphine Ligands

Six new benzimidazolylphosphine N^P ligands were synthesized by introducing different substituents.Through regulating electronic effect of the ligands,the photo-luminescence properties of Cu(I)complexes could be improved apparently.Molecular structures of ligands L(L1 ~ L6)were as follows:The reaction of cuprous halide(CuX,X = I,Br,Cl)with L1~L6 and triphenylphosphine obtained six series of total eighteen novel mononuclear Cu(I)complexes.Then structures of these complexes were confirmed by NMR,elemental analysis and X-ray single crystal diffraction.Their optical properties and electrochemical properties were carefully investigated.Also several representative complexes were calculated through density functionary theory(DFT)to elucidate the luminescent properties of the complexes at the molecular level.X-ray crystallographic studies reveal that the obtained complexes were all deformed tetrahedral geometries around Cu(I)centre.The emissions of these complexes from green to yellow light(from 531 nm to 587 nm)were obtained by controlling the substituents and halogen anions.When the ligands were the same,the emission peaks follow the order of Cu LI < Cu LBr < Cu LCl.The luminescent quantum yield(Φ)of iodine complexes were relatively high,among them Cu L2 I had the highest quantum yield of 88.29%.Emission peaks of Cu L1 Br,Cu L1 Cl and Cu L4 Cl at 77 K red shifted compared with that at 293 K.ΔE(S1-T1)of Cu L1 Br,Cu L1 Cl and Cu L4 Cl were estimated less than 500 cm-1,so their luminescences belonged to thermally activated delayed fluorescence(TADF).The other complexes’ emission peaks at 77 K blue shifted compared with that at 293 K,and their luminescences were phosphorescence in nature.The emission decay time of all the complexes were between 2.9 μs and 65.7 μs.Electrochemical analysises reveal that the presence of electron-withdrawing substituents and iodine anion can elevate the oxidation potentials of the complexes.However,the natures of the substituents have little influence on the HOMO and LUMO levels of the complexes.The theoretical calculations showed that luminescence of Cu(I)complexes were mainly from XLCT and MLCT transitions.Contribution ratios of halogen to complexes’ HOMO decreased sequentially with the order of I,Br and Cl,while the contribution ratio of Cu(I)was on the contrary.The results illustrate that MLCT gradually increased and XLCT decreased with the order of I,Br and Cl.