Iridium(III) complexes with cyclometalated styrylbenzoimidazole ligands: Synthesis, electrochemistry and as highly efficient emitters for organic light-emitting diodes

Two phosphorescent iridium complexes (psbi)2Ir(acac) and (ppbi)2Ir(acac) (psbi = 1-phenyl-2-styryl-1H-benzo[d]imidazole, ppbi = 1-phenyl-2-(1-phenylprop-1-en-2-yl)-1H-benzo[d]imidazole, acac = acetylacetonate) were synthesized, and their photophysical, electrochemical and electroluminescent properties were also studied. Organic light-emitting devices with these two complexes as dopant emitters having the structure ITO/NPB (10 nm)/TCTA (20 nm)/x%Ir:CBP (y nm)/BCP (10 nm)/LiF (1 nm)/Al (100 nm) were fabricated. The device based on (psbi)2Ir(acac) exhibited a maximum brightness of 56,162 cd m−2, while the device based on (ppbi)2Ir(acac) gave a maximum brightness of 31,232 cd m−2. At high brightness of 1000 cd m−2 and 10,000 cd m−2, high current efficiencies of 25.7 cd A−1 and 20.7 cd A−1 were achieved, respectively, for the (psbi)2Ir(acac)-based EL device. For the EL device based on (ppbi)2Ir(acac), current efficiencies of 20.1 cd A−1 at 1000 cd m−2 and 14.2 cd A−1 at 10,000 cd m−2 were observed.