title: Homoleptic cyclometalated iridium complexes with highly efficient red phosphorescence and application to organic light-emitting diode.
abstract: Phosphorescence studies of a series of facial homoleptic cyclometalated iridium(III) complexes have been carried out. The complexes studied have the general structure Ir(III)(C-N)(3), where (C-N) is a monoanionic cyclometalating ligand: 2-(5-methylthiophen-2-yl)pyridinato, 2-(thiophen-2-yl)-5-trifluoromethylpyridinato, 2,5-di(thiophen-2-yl)pyridinato, 2,5-di(5-methylthiophen-2-yl)pyridinato, 2-(benzo[b]thiophen-2-yl)pyridinato, 2-(9,9-dimethyl-9H-fluoren-2-yl)pyridinato, 1-phenylisoquinolinato, 1-(thiophen-2-yl)isoquinolinato, or 1-(9,9-dimethyl-9H-fluoren-2-yl)isoquinolinato. Luminescence properties of all the complexes at 298 K in toluene are as follows: quantum yields of phosphorescence Phi(p) = 0.08-0.29, emission peaks lambda(max) = 558-652 nm, and emission lifetimes tau = 0.74-4.7 micros. Bathochromic shifts of the Ir(thpy)(3) family [the complexes with 2-(thiophen-2-yl)pyridine derivatives] are observed by introducing appropriate substituents, e.g., methyl, trifluoromethyl, or thiophen-2-yl. However, Phi(p) of the red emissive complexes (lambda(max) > 600 nm) becomes small, caused by a significant decrease of the radiative rate constant, k(r). In contrast, the complexes with the 1-arylisoquinoline ligands are found to have marked red shifts of lambda(max) and very high Phi(p) (0.19-0.26). These complexes are found to possess dominantly (3)MLCT (metal-to-ligand charge transfer) excited states and have k(r) values approximately 1 order of magnitude larger than those of the Ir(thpy)(3) family. An organic light-emitting diode (OLED) device that uses Ir(1-phenylisoquinolinato)(3) as a phosphorescent dopant produces very high efficiency (external quantum efficiency eta(ex) = 10.3% and power efficiency 8.0 lm/W at 100 cd/m(2)) and pure-red emission with 1931 CIE (Commission Internationale de L'Eclairage) chromaticity coordinates (x = 0.68, y = 0.32).
authors.affiliation: OL Project, Canon Inc., Atsugi, Kanagawa 243-0193, Japan. tsuboyama.akira@canon.co.jp
authors.forename: Akira
authors.initials: A
authors.lastname: Tsuboyama
authors.forename: Hironobu
authors.initials: H
authors.lastname: Iwawaki
authors.forename: Manabu
authors.initials: M
authors.lastname: Furugori
authors.forename: Taihei
authors.initials: T
authors.lastname: Mukaide
authors.forename: Jun
authors.initials: J
authors.lastname: Kamatani
authors.forename: Satoshi
authors.initials: S
authors.lastname: Igawa
authors.forename: Takashi
authors.initials: T
authors.lastname: Moriyama
authors.forename: Seishi
authors.initials: S
authors.lastname: Miura
authors.forename: Takao
authors.initials: T
authors.lastname: Takiguchi
authors.forename: Shinjiro
authors.initials: S
authors.lastname: Okada
authors.forename: Mikio
authors.initials: M
authors.lastname: Hoshino
authors.forename: Kazunori
authors.initials: K
authors.lastname: Ueno