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