title: 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=SiPh(3), GePh(3), NPh(2), POPh(2), OPh, SPh, SO(2)Ph, 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 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 (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-SiPh(3))(3)], 13.9 %, 60.8 cd A(-1), 49.1 Lm W(-1) for [Ir(ppy-NPh(2))(3)], and 10.1 %, 37.6 cd A(-1), 26.1 Lm W(-1) for [Ir(ppy-SO(2)Ph)(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.
authors.affiliation: Department of Chemistry and Centre for Advanced Luminescence Materials, Hong Kong Baptist University, Waterloo Road, Kowloon Tong, Hong Kong, P.R. China.
authors.forename: Guijiang
authors.initials: G
authors.lastname: Zhou
authors.forename: Qi
authors.initials: Q
authors.lastname: Wang
authors.forename: Cheuk-Lam
authors.initials: CL
authors.lastname: Ho
authors.forename: Wai-Yeung
authors.initials: WY
authors.lastname: Wong
authors.forename: Dongge
authors.initials: D
authors.lastname: Ma
authors.forename: Lixiang
authors.initials: L
authors.lastname: Wang
authors.forename: Zhenyang
authors.initials: Z
authors.lastname: Lin