New rhenium complexes containing 4,5-diazafluorene ligand for high-efficiency green electrophosphorescence

Two novel tricarbonyl rhenium complexes featuring 4,5-diazafluorene (DF)-based ligand, i.e., Re-DF and Re-EPDF (EPDF, 9,9-di-(4-ethoxyphenyl)-9-H-4,5-diazafluorene), were designed, synthesized and characterized by 1H NMR and mass spectroscopy. The green organic light-emitting diodes (OLEDs) based on these complexes with the configuration of ITO/m-MTDATA (10 nm)/NPB (20 nm)/CBP: Re-complex (30 nm)/Bphen (10 nm)/Alq3 (30 nm)/LiF (1 nm)/Al (100 nm) were fabricated. The devices based on Re-DF showed a maximum current efficiency of 20.7 cd/A and a peak luminance of 2506 cd/cm2, respectively. And the Re-EPDF doped devices exhibited a maximum current efficiency of 13.5 cd/A and a luminance of 3208 cd/cm2. Moreover, the 20 wt.% Re-EPDF doped device still provided a maximum current efficiency of 13.2 cd/A.