Deep-Red Light-Emitting Phosphorescent Dendrimer Encapsulated Tris-[2-benzo[b]thiophen-2-yl-pyridyl] Iridium (III) Core for Light-Emitting Device Applications

Abstract

New deep-red light-emitting phosphorescent dendrimers with hole-transporting carbazole dendrons were synthesized by reacting tris(2-benzo[b]thiophen-2-yl-pyridyl) iridium (III) complex with carbazolyl dendrons by DCC-catalyzed esterification. The resulting first-, second-, and third-generation dendrimers were found to be highly efficient as solution-processable emitting materials and for use in host-free electrophosphorescent light-emitting diodes. We fabricated a host-free dendrimer EL device with configuration ITO/PEDOT:PSS (40 nm)/dendrimer (55 nm)/BCP (10 nm)/Alq(3) (40 nm)/LiF (1 nm)/Al (100 nm) and characterized the device performance. The multilayered devices showed luminance of 561 cd/m(2) at 383.4 mA/cm(2) (12 V) for 15, 1302 cd/m(2) at 321.3 mA/cm(2) (14 V) for 16, and 422 cd/m(2) at 94.4 m.A/cm(2) (18 V) for 17. The third-generation dendrimer, 17 (n(ext) = 6.12% at 7.5 V), showed the highest external quantum efficiency (EQE) with an increase in the density of the light-harvesting carbazole dendron. Three dendrimers exhibited considerably pure deep-red emission with CIE 1931 (Commission International de L'Eclairage) chromaticity coordinates of x = 0.70, y = 0.30. The CIE coordinates remained very stable with the current density. The integration of rigid hole-transporting dendrons and phosphorescent complexes provides a new route to design highly efficient solution-processable materials for dendrimer light-emitting diode (DLED) applications. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7517-7533, 2008