Synthesis, structure, photo- and electro-luminescence of an iridium(iii) complex with a novel carbazole functionalized β-diketone ligand

Abstract

A new iridium complex containing coumarin derivative as a cyclometalated ligand (¹L) and a carbazole-functionalized β-diketonate (²L) as the ancillary ligand, namely, Ir(III)bis(3-(pyridin-2-yl)coumarinato-N,C⁴)(1-(9-butyl-9H-carbazol-3-yl)-4,4,4-trifluoro-butane-1,3-dionato-O,O) (Ir(¹L)₂(²L)), was synthesized. The crystal structure of Ir(¹L)₂(²L) was determined via combined wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM), which showed π–π the interactions of Ir(¹L)₂(²L) molecules stacking along the crystal axes. The doped light-emitting diodes using this novel Ir(¹L)₂(²L) complex as the phosphorescent dopant were fabricated. At a Ir(¹L)₂(²L) concentration of 6.0 wt%, a green-yellow emitting OLED was achieved with a maximum external quantum efficiency (EQE) of 6.11% and a maximum luminous efficiency of 22.55 cd A⁻¹ at the current density of 6.06 mA cm⁻², and a maximum luminance of 6653 cd m⁻² at 10.7 V. Furthermore, two reference complexes Ir(¹L)₂(acac) and Ir(¹L)₂(TTA) were also used as emitters to fabricate OLED devices with the same device configuration. The maximum luminous efficiency of Ir(¹L)₂(acac) doped device was measured to be 20.04 cd A⁻¹ at 2.15 mA cm⁻² (10.0 wt%), while the doped device of Ir(¹L)₂(TTA) had a maximum luminous efficiency of 16.59 cd A⁻¹ at 1.36 mA cm⁻². The better performances of Ir(¹L)₂(²L) doped devices could be largely attributed to an improved hole-transporting property due to the introduction of the carbazole moiety.