title: Iridium(III) complexes with orthometalated quinoxaline ligands: subtle tuning of emission to the saturated red color.
abstract: Rational design and syntheses of four iridium complexes (1-4) bearing two substituted quinoxalines and an additional 5-(2-pyridyl) pyrazolate or triazolate as the third coordinating ligand are reported. Single-crystal X-ray diffraction studies of 1 reveal a distorted octahedral geometry, in which two dpqx ligands adopt an eclipse configuration, for which the quinoxaline N atoms and the C atoms of orthometalated phenyl groups are located at the mutual trans- and cis-positions, respectively. The lowest absorption band for all complexes consists of a mixture of heavy-atom Ir(III)-enhanced 3MLCT and 3pipi* transitions, and the phosphorescent peak wavelength can be fine-tuned to cover the spectral range of 622-649 nm with high quantum efficiencies. The cyclic voltammetry was measured, showing a reversible, metal-centered oxidation with potentials at 0.76-1.03 V, as well as two reversible reduction waves with potentials ranging from -1.61 to -2.06 V, attributed to the sequential addition of two electrons to the more electron-accepting heterocyclic portion of two distinctive cyclometalated C/N ligands. Complex 1 was used as the representative example to fabricate the red-emitting PLEDs by blending it into a PVK-PBD polymer mixture. The devices exhibited the characteristic emission profile of 1 with peak maxima located at 640 nm. The maximum external quantum efficiency was 3.15% ph/el with a brightness of 1751 cd/m2 at a current density of 67.4 mA/cm2, and the maximum brightness of 7750 cd/m2 was achieved at the applied voltage of 21 V and with CIE coordinates of (0.64, 0.31).
authors.affiliation: Department of Chemistry, National Tsing Hua University, Hsinchu 300, Taiwan.
authors.forename: Fu-Ming
authors.initials: FM
authors.lastname: Hwang
authors.forename: Hsing-Yi
authors.initials: HY
authors.lastname: Chen
authors.forename: Po-Shen
authors.initials: PS
authors.lastname: Chen
authors.forename: Chao-Shiuan
authors.initials: CS
authors.lastname: Liu
authors.forename: Yun
authors.initials: Y
authors.lastname: Chi
authors.forename: Ching-Fong
authors.initials: CF
authors.lastname: Shu
authors.forename: Fang-Iy
authors.initials: FI
authors.lastname: Wu
authors.forename: Pi-Tai
authors.initials: PT
authors.lastname: Chou
authors.forename: Shie-Ming
authors.initials: SM
authors.lastname: Peng
authors.forename: Gene-Hsiang
authors.initials: GH
authors.lastname: Lee