Synthesis, Structural Characterization, and Electrophosphorescent Properties of Rhenium(I) Complexes Containing Carrier-Transporting Groups

Two novel diimine rhenium(I) carbonyl complexes with the formula [Re(CO)3(L)Br], where L = 1-(4-5‘-phenyl-1,3,4-oxadiazolylbenzyl)-2-pyridinylbenzoimidazole (1) and 1-(4-carbazolylbutyl)-2-pyridinylbenzoimidazole (2), have
been successfully synthesized and characterized by elemental analysis, 1H NMR, and IR spectra. Their
electrochemical, photophysical, and electroluminescent behaviors, along with the X-ray crystal structure analysis of
2, are also described. White electrophosphorescent devices were fabricated using 1 and 2 as emitters. The devices
based on carbazole-containing (hole-transporting group) 2 with the structure ITO/m-MTDATA (30 nm)/NPB (20
nm)/2:CBP (8%, 30 nm)/Bphen (20 nm)/Alq3 (20 nm)/LiF (0.8 nm)/Al (200 nm) exhibit Commission Internationale
de L'Eclairage coordinates of x = 0.34, y = 0.33 with a maximum brightness of 2300 cd/m2 at 580 mA/cm2.
When a brightness of 1500 cd/m2 appears at 230 mA/cm2, the devices based on 10 wt % 2 still possess 56% of
the maximum efficiency which appeared at 2.7 mA/cm2. These performances are among the best reported for
devices using Re(I) complexes as emitters. By comparison of the electroluminescent properties of the devices
based on 1 and 2, we conclude that the introduction of the carbazole group into the ligand improves the performance
of 1-doped devices.