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

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)(3)Ir 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)(3)Ir and (mCP)(2)(bpp)Ir in their diluted solutions were 91% and 84%, respectively. They showed high PLQEs of 49% for (mCP)(3)Ir 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)(3)Ir 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)(3)Ir and 5.4% for (mCP)(2)(bpp)Ir at 100 cd/m(2). (C) 2009 Elsevier B.V. All rights reserved.