Synthesis and characterization of homoleptic triply cyclometalated iridium (III) complex containing 6-(pyridin-2-yl)isoquinoline moiety for solution-processable orange-phosphorescent organic light-emitting diodes

Abstract

The design and synthesis of a novel homoleptic triply cyclometalated iridium(III) complex containing the 6-(pyridin-2-yl)isoquinoline moiety [Ir(pyiq)(3)] was demonstrated for the first time. The performance of a phosphorescent organic light emitting diode (PHOLED) based on Ir(pyiq)(3) is described with adoption of tris(4-carbazoyl-9-ylphenyl)amine (TCTA) and 2,2',2 ''-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) which are co-host materials showing excellent compatibilities as well as CBP host with the prepared phosphorescent dopants. The photoluminescence (PL) of Ir(pyiq)(3) produced orange emission with maximum emission peak at 583 nm. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital energy (LUMO) levels of Ir(pyiq)(3) were 5.41 eV and 3.20 eV. An optimized solution-processed device doped with Ir(pyiq)(3) had a maximum external quantum efficiency (EQE) of 8.71% and a maximum current efficiency (CE) of 22.51 cd/A. This correspond to 17% higher efficiency than that with bis(2-phenylbenzothiozolato-N,C-2') iridium(acetylacetonate) (bt)(2)Ir(acac), which is commonly used in orange PHOLEDs. This study rationalizes the promising application of new trimeric organometallic complex that possesses isoquinoline and pyridine in solution-processed PHOLEDs with good quantum and power efficiency.