Homoleptic mer-Ir(III) complexes for highly efficient solution-processable green phosphorescent organic light-emitting diodes with high current efficiency
Two new highly efficient homoleptic green emitting meridional iridium (III) complexes namely, mer-tris[5-hexyl-8-trifluoromethyl-5H-benzo(c)(1,5)naphthyridin-6-one]iridium(III) (mer-Ir1) and mer-tris[5-ethylhexyl-8-trifluoromethyl-5H-benzo(c)(1,5)naphthyridin-6-one]iridium(III) (mer-Ir2) were designed and synthesized at high temperature. These new Ir(III) complexes consist of amide bridged trifluoromethyl substituted phenyl pyridine skeleton with longer alkyl chain. Interestingly, both complexes show bright green emission (λmax = 528 nm) with high photoluminance quantum yield of 42% and 51% in solution at room temperature. Their thermal, photophysical, electrochemical, and electroluminescent (EL) properties are fully investigated. Both complexes were used as dopant for solution-processed green phosphorescence organic light-emitting diodes (PHOLEDs). Notably, the device using mer-Ir2 as new green dopant exhibits excellent EL performance with a maximum external quantum efficiency (EQEmax) of 20.03% and maximum current efficiency (CEmax) of 67.81 cd A-1. To the best of our knowledge, this is the first time here we reported that particularly Ir(C^N)3 based mer-Ir(III) isomers show excellent EL performance with high luminous efficiency in the green region via solution-processed PHOLEDs.