title: Phosphorescent iridium(III) complexes with nonconjugated cyclometalated ligands.
abstract: A series of blue phosphorescent iridium(III) complexes 1-4 with nonconjugated N-benzylpyrazole ligands were synthesized and their structural, electrochemical, and photophysical properties were investigated. Complexes 1-4 exhibit phosphorescence with yields of 5-45 % in degassed CH2Cl2. Of the compounds, 1 showed emission that was nearly true blue at 460 nm with a lack of vibronic progression. These photophysical data clearly demonstrate that the methylene spacer of the cyclometalated N-benzylpyrazole chelate effectively interrupts the pi conjugation upon reacting with a third L X chelating chromophore. This gives a feasible synthesis for the blue phosphorescent complexes with a sufficiently large energy gap. In another approach, these complexes were investigated for their suitability for the host material in phosphorescent OLEDs. The device was synthesized by using 1 as the host for the green-emitting [Ir(ppy)3] dopant, which exhibits an external quantum conversion efficiency (EQE) of up to 11.4 % photons per electron (and 36.6 cdA(-1)), with 1931 Commission Internationale de L'Eclairage (CIE) coordinates of (0.30, 0.59), a peak power efficiency of 21.7 lmW(-1), and a maximum brightness of 32000 cdm(-2) at 14.5 V. At the practical brightness of 100 cdm(-2), the efficiency remains above 11 % and 18 lmW(-1), demonstrating its great potential as the host material for phosphorescent organic light-emitting diodes.
authors.affiliation: Department of Chemistry, National Tsing Hua University, Hsinchu 300, Taiwan.
authors.forename: Yi-Hwa
authors.initials: YH
authors.lastname: Song
authors.forename: Yuan-Chieh
authors.initials: YC
authors.lastname: Chiu
authors.forename: Yun
authors.initials: Y
authors.lastname: Chi
authors.forename: Yi-Ming
authors.initials: YM
authors.lastname: Cheng
authors.forename: Cheng-Hsuan
authors.initials: CH
authors.lastname: Lai
authors.forename: Pi-Tai
authors.initials: PT
authors.lastname: Chou
authors.forename: Ken-Tsung
authors.initials: KT
authors.lastname: Wong
authors.forename: Ming-Han
authors.initials: MH
authors.lastname: Tsai
authors.forename: Chung-Chih
authors.initials: CC
authors.lastname: Wu