title: A new class of sky-blue-emitting Ir(III) phosphors assembled using fluorine-free pyridyl pyrimidine cyclometalates: application toward high-performance sky-blue- and white-emitting OLEDs.
abstract: Two pyrimidine chelates with the pyridin-2-yl group residing at either the 5- or 4-positions are synthesized. These chelates are then utilized in synthesizing of a new class of heteroleptic Ir(III) metal complexes, namely [Ir(b5ppm)2(fppz)] (1), [Ir(b5bpm)2(fppz)] (2), [Ir(b4bpm)2(fppz)] (3), and [Ir(b5bpm)(fppz)2] (4), for which the abbreviations b5ppm, b5bpm, b4bpm, and fppz represent chelates derived from 2-t-butyl-5-(pyridin-2-yl)pyrimidine, 2-t-butyl-5-(4-t-butylpyridin-2-yl)pyrimidine, 2-t-butyl-4-(4-t-butylpyridin-2-yl)pyrimidine, and 3-trifluoromethyl-5-(pyridin-2-yl) pyrazole, respectively. The single crystal X-ray structural analyses were executed on 1 to reveal their coordination arrangement around the Ir(III) metal element. The 5-substituted pyrimidine complexes 1, 2, and 4 exhibited the first emission peak wavelength (λmax) located in the range 452-457 nm with high quantum yields, whereas the emission of 3 with 4-substituted pyrimidine was red-shifted substantially to longer wavelength with λmax = 535 nm. These photophysical properties were discussed under the basis of computational approaches, particularly the relationship between emission color and the relative position of nitrogen atoms of pyrimidine fragment. For application, organic light-emitting diodes (OLEDs) were also fabricated using 2 and 4 as dopants, attaining the peak external quantum, luminance, and power efficiencies of 17.9% (38.0 cd/A and 35.8 lm/W) and 15.8% (30.6 cd/A and 24.8 lm/W), respectively. Combining sky blue-emitting 2 and red-emitting [Os(bpftz)2(PPh2Me)2] (5), the phosphorescent white OLEDs were demonstrated with stable pure-white emission at CIE coordinate of (0.33, 0.34), and peak luminance efficiency of 35.3 cd/A, power efficiency of 30.4 lm/W, and external quantum efficiency up to 17.3%.
authors.affiliation: Department of Photonics Engineering, Yuan Ze University, Chung-Li 32003, Taiwan. chc@saturn.yzu.edu.tw
authors.forename: Chih-Hao
authors.initials: CH
authors.lastname: Chang
authors.forename: Zih-Jyun
authors.initials: ZJ
authors.lastname: Wu
authors.forename: Chuan-Hao
authors.initials: CH
authors.lastname: Chiu
authors.forename: Yi-Hu
authors.initials: YH
authors.lastname: Liang
authors.forename: Yu-Shan
authors.initials: YS
authors.lastname: Tsai
authors.forename: Jia-Ling
authors.initials: JL
authors.lastname: Liao
authors.forename: Yun
authors.initials: Y
authors.lastname: Chi
authors.forename: Hsi-Ying
authors.initials: HY
authors.lastname: Hsieh
authors.forename: Ting-Yi
authors.initials: TY
authors.lastname: Kuo
authors.forename: Gene-Hsiang
authors.initials: GH
authors.lastname: Lee
authors.forename: Hsiao-An
authors.initials: HA
authors.lastname: Pan
authors.forename: Pi-Tai
authors.initials: PT
authors.lastname: Chou
authors.forename: Jin-Sheng
authors.initials: JS
authors.lastname: Lin
authors.forename: Meu-Rurng
authors.initials: MR
authors.lastname: Tseng