Synthesis, structures, DFT studies and luminescent properties of copper(I)-diimine complexes and application in yellow-green light-emitting diode

A series of copper(I) - diimine complexes, [Cu(bdpp)(bpy)]BF 4 ( 1 ), [Cu(bdpp) (pen)]BF 4 ( 2 ), [Cu(bdpp)(damp)]BF 4 ( 3 ), [Cu(bdpp)(pen)]BF 4 ( 4 ) (bdpp  =  4,6-bis-(biphenyl phosphino) phenoxazine, bpy = 2,2′-bipyridine, phen = 1,10-Phenanthroline, dmp = 2,9-dimethyl-1,10-phenanthroline, bphen = 4,7-diphenyl-1,10-phenanthroline), have been synthesized and characterized by IR, 1 H NMR, 31 P NMR, XRD and X-ray crystal structure analysis. Structural analysis reveals that each Cu + in 1 – 4 is four-coordinated by two N atoms and two P atoms and adopts a distorted tetrahedral geometry. DFT calculations show that the HOMOs in 1 – 4 are mainly comprised of bdpp and copper d–orbitals, while the LUMOs are mainly dominated by diimine ligands. Calculation of atomic charges indicates that the charges of the central Cu atoms in 1 – 4 are less than + 1, and the diimine ligands may be the key to the metal charge transfer to the coordinated atom. In 1 – 4 , the maximum phosphorescent lifetimes and quantum yields are up to 349 μs and 22%, respectively. Moreover, complex 3 is used for fabricating the LED device, showing a decent performance with the maximum EQE of 11%.