Browsing by Author "Wong, Man Shing"

Now showing 1 - 6 of 6

Efficient deep-blue organic light-emitting diodes: Arylamine-substituted oligofluorenes
(2007-11-05)
Gao, Zhi Qiang
;
Li, Zhong Hui
;
Xia, Ping Fan
;
Wong, Man Shing
;
Cheah, Kok Wai
Novel deep-blue-light-emitting diphenylamino and triphenylamino end-capped oligofluorenes were synthesized by double palladium-catalyzed Suzuki cross- coupling of dibromo-oligofluorene with the corresponding boronic acid as a key step. These oligofluorenes exhibit deep-blue emission (lambda(em)(max) = 429-432 nm), low and reversible electrochemical oxidation (highest occupied molecular orbital = 5.15-5.20 eV), high fluorescence quantum yield (Phi(FL) = 0.61-0.93), and good thermal properties (glass-transition temperature, T-g = 99-195 degrees C and decomposition temperature, T-dec > 450 degrees C). Remarkably, saturated deep-blue organic light-emitting diodes, made from these oligofluorenes as dopant emitters, have been achieved with excellent performance and maximum efficiencies up to 2.9 cd A(-1) at 2 mA cm(-2) (external quantum efficiency of 4.1 %) and with Commission Internationale de l'Eclairage (x,y) coordinates of (0.152,0.08), which is very close to the National Television System Committee standard blue.
High efficiency and small roll-off electrophosphorescence from a new iridium complex with well-matched energy levels
(2008-02-18)
Gao, Zhi Qiang
;
Mi, Bao Xiu
;
Tam, Hoi Lam
;
Cheah, Kok Wai
;
Chen, Chin Hsin
Phenylpyridazine ligands coordinating to the iridium(III) atom yield a thermally stable (5 % weight loss at 439 degrees C) homoleptic iridium complex with a high phosphorescent quantum yield (0.32 at room temperature). This material has well-matched energy levels with the host, and highly efficient electrophosphorescence (52 cd A(-1); see figure) with a small roll-off (23 % at 70 mA cm(-2)) in device efficiency is achieved.
New Host Containing Bipolar Carrier Transport Moiety for High-Efficiency Electrophosphorescence at Low Voltages
(2009-02-09)
Gao, Zhi Qiang
;
Luo, Meiming
;
Sun, Xiao Hua
;
Tam, Hoi Lam
;
Wong, Man Shing
A new host material for use in phosphorescent OLEDs with desirable electronic properties has been synthesized. The material exhibits superior carrier-transport properties, a narrow optical band gap, relatively high triplet energy, and high thermal stability. It is synthesized by integrating hole-transporting carbazole groups into an electron-transporting phenanthroline core (see figure), and is demonstrated to be an excellent host for phosphorescent dopant emitters.
p-Doped p-phenylenediamine-substituted fluorenes for organic electroluminescent devices
(2009-07-01)
Gao, Zhi Qiang
;
Xia, Ping Fan
;
Lo, Pik Kwan
;
Mi, Bao Xiu
;
Tam, Hoi Lam
Two novel p-phenylenediamine-substituted fluorenes have been designed and synthesized. Their applications as hole injection materials in organic electroluminescent devices were investigated. These materials show a high glass transition temperature and a good hole-transporting ability. It has been demonstrated that the 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) doped p-phenylene-diamine-substituted fluorenes, in which F4-TCNQ acts as p-type dopant, are highly conducting with a good hole-transporting property. The organic light emitting devices (OLEDs) utilizing these F4-TCNQ-doped materials as a hole injection layer were fabricated and investigated. The pure Alq(3)-based OLED device shows a current efficiency of 5.2 cd/A at the current density of 20 mA/cm(2) and the operation lifetime is 1500 h with driving voltage increasing only about 0.7 mV/h. The device performance and stability of this hole injection material meet the benchmarks for the commercial requirements for OLED materials. (C) 2009 Elsevier B.V. All rights reserved.
Strong Luminescent Iridium Complexes with (CN)-N-boolean AND=N Structure in Ligands and Their Potential in Efficient and Thermally Stable Phosphorescent OLEDs
(2009-01-19)
Mi, Boo Xiu
;
Wang, Peng Fei
;
Gao, Zhi Qiang
;
Lee, Chun Sing
;
Lee, Shuit Tong
Homoleptic iridium complexes with (CN)-N-boolean AND=N type ligands, i.e., 1,4-bis (phenyl) phthalazine (BPPa) and 3,6-bis(phenyl)pyridazine (BPPya), are strong phosphorescents, easy to synthesize, and thermally stable, thus having great potential in optical electronic applications, as demonstrated in lr(BPPa)(3)-based OLED devices. A quantum chemistry study shows that (CN)-N-boolean AND=N type ligands can bond to Ir more strongly.
Strong Luminescent Iridium Complexes with C(boolean AND)N=N Structure in Ligands and Their Potential in Efficient and Thermally Stable Phosphorescent OLEDs
(2009-01-19)
Mi, Boo Xiu
;
Wang, Peng Fei
;
Gao, Zhi Qiang
;
Lee, Chun Sing
;
Lee, Shuit Tong
Homoleptic iridium complexes with C(boolean AND)N=N type ligands, i.e., 1,4-bis (phenyl) phthalazine (BPPa) and 3,6-bis(phenyl)pyridazine (BPPya), are strong phosphorescents, easy to synthesize, and thermally stable, thus having great potential in optical electronic applications, as demonstrated in lr(BPPa)(3)-based OLED devices. A quantum chemistry study shows that C(boolean AND)N=N type ligands can bond to Ir more strongly.