Robust tris-cyclometalated iridium(III) phosphors with ligands for effective charge carrier injection/transport: Synthesis, redox, photophysical, and electrophosphorescent behavior

Abstract

With the target to design and develop new functionalized green triplet light emitters that possess distinctive electronic properties for robust and highly efficient phosphorescent organic light-emitting diodes (PHOLEDs), a series of bluish-green to yellow-green phosphorescent tris-cyclometalated homoleptic iridium(III) complexes [Ir(ppy-X)3] (X = SiPh3, GePh3, NPh2, POPh2, OPh, SPh, SO 2Ph, Hppy = 2-phenylpyridine) have been synthesized and fully characterized by spectroscopic, redox, and photophysical methods. By chemically manipulating the lowest triplet-state character of Ir(ppy)3 with some functional main-group 14-16 moieties on the phenyl ring of ppy, a new family of metallophosphors with high-emission quantum yields, short triplet-state lifetimes, and good hole-injection/holetransporting or electron-injection/ electron-transporting properties can be obtained. Remarkably, all of these IrIII complexes show outstanding electrophosphorescent performance in multilayer doped devices that surpass that of the state-of-the-art green-emitting dopant Ir(ppy)3. The devices described herein can reach the maximum external quantum efficiency (ηext) of 12.3%, luminance efficiency (ηL) of 50.8 cdA-1, power efficiency (ηp) of 36.9 LmW-1 for [Ir(ppy-SiPh 3)3], 13.9%, 60.8 cdA-1, 49.1 LmW-1 for [Ir(ppy-NPh2)3], and 10.1%, 37.6 cdA-1, 26.1 Lm W-1 for [Ir(ppy-SO2Ph)3]. These results provide a completely new and effective strategy for carrier injection into the electrophosphor to afford high-performance PHOLEDs suitable for various display applications. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.