Synthesis,photoluminescence and electroluminescence properties of iridium complexes with bulky carbazole dendrons

We synthesized solution-processable iridium complexes having bulky carbazole dendrons, fac-tris2-{3-(3,5-bis(3,6-di-n-butylcarbazol-9-yl)phenyl)Phenyl)pyridine]iridium (III) (mCP)₃Ir and fac-bis2-{3-(3,5-bis(3,6-di-n-butylcarbazol-9-yl)phenyl)phenyl}pyridine]2-{3-(3,5-di(4-pyridyl)phenyl)phenyl}pyridine]iridium (III) (mCP)₂(bpp)Ir. Photoluminescence quantum efficiencies (PLQEs) of (mCP)₃Ir and (mCP)₂(bpp)Ir in their diluted solutions were 91% and 84%, respectively. They showed high PLQEs of 49% for (mCP)₃Ir and 29% for (mCP)₂(bpp)Ir even in a neat film. The triplet exciton energy level of the dendronized ligand (2.8 eV), 2-3-{3,5-bis(3,6-di-n-butylcarbazol-9-yl)phenyl}]pyridine 10, and the dendron (2.9 eV), 3,5-bis(3,6-di-n-butylcarbazol-9-yl)benzene 7, are enough higher than that of the core complex Ir(ppy)₃ (2.6 eV). External quantum efficiency (EQE) of single layer light-emitting device with (mCP)₂(bpp)Ir was much higher than that of (mCP)₃Ir because of better affinity of (mCP)₂(bpp)Ir to cathode metal. When an electron transporting and hole-blocking material was used, the EQEs of double layer devices were dramatically improved to 8.3% for (mCP)₃Ir and 5.4% for (mCP)₂(bpp)Ir at 100 cd/m².