Robust Tris-Cyclometalated Iridium(III) Phosphors with Ligands for Effective Charge Carrier Injection/Transport: Synthesis, Redox, Photophysical, and Electrophosphorescent Behavior

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, SO2Ph, 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/hole-transporting or electron-injection/electron-transporting properties can be obtained. Remarkably, all of these Ir-III complexes show outstanding electrophosphorescent performance in multi-layer 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 (eta(ext)) of 12.3\%, luminance efficiency (eta(L)) of 50.8 cd A(-1), power efficiency (eta(p)) of 36.9 Lm W-1 for [Ir(ppy-SiPh3)(3)], 13.9\%, 60.8 cd A(-1), 49.1 Lm W-1 for [Ir(ppy-NPh2)(3)], and 10.1\%, 37.6 cd A(-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