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

Abstract

We synthesized solution-processable iridium complexes having bulky carbazole dendrons, fac-tris[2-{3-(3,5-bis(3,6-di- n-butylcarbazol-9-yl)phenyl)Phenyl)pyridine]iridium (III) (mCP) 3Ir and fac-bis[2-{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/m 2.