Greenish yellow organic light emitting devices based on novel iridium complexes containing 2-cyclohexenyl-1-phenyl-1H-benzo[d]imidazole

• Iridium complexes (cyclopbi)2Iracac and (cyclopbi)2IrCF3 were synthesized.
• Both the complexes show bright greenish yellow phosphorescence at room temperature.
• High efficiency OLEDs were obtained with maximum current efficiency 22.3 cd/A.

2-Cyclohexenyl-1-phenyl-1H-benzo[d]imidazole (Hcyclopbi) and its heterocyclometalated iridium complexes bis[2-cyclohexenyl-1-phenyl-1H-benzo[d]imidazole](acetylacetonate)iridium(III) [(cyclopbi)2Iracac] and bis[2-cyclohexenyl-1-phenyl-1H-benzo[d]imidazole][2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridinate]iridium(III) [(cyclopbi)2IrCF3] were firstly designed and synthesized. Owing to the strong electron withdrawing ability of 2-(3-(trifluoromethyl)-1H-pyrazol) compared to that of acetylacetonate, blue shifted phosphorescence 542 nm was obtained for (cyclopbi)2IrCF3 compared to that of (cyclopbi)2Iracac 545 nm with photoluminescence quantum yields (φ) 0.22 and 0.25, respectively, as well the highest occupied molecular orbit (HOMO) energy level was estimated to be −5.10 eV for (cyclopbi)2IrCF3, 0.19 eV lower than that of −4.91 eV for (cyclopbi)2Iracac. When (cyclopbi)2Iracac was doped into 4,4′-bis(9H-carbazol-9-yl)biphenyl (CBP) as the emitting layer, high efficiency organic light emitting devices (OLEDs) were obtained with maximum current efficiency (ηc) 22.3 cd/A at 3.1 mA/cm2 and maximum brightness 16,300 cd/m2 at 171.6 mA/cm2, which were comparable to those of bis(2-phenylpyridine)(acetylacetonate)iridium(III) [(ppy)2Iracac] with the same device structure. This results indicate that (cyclopbi)2Iracac and (cyclopbi)2IrCF3 are potential phosphorescent dyes used for OLEDs.

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