Browsing by Author "Su, HJ"

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Color tuning of a light-emitting polymer: Polyfluorene-containing pendant amino-substituted distyrylarylene units
(2005-07-01)
Su, HJ
;
Wu, FI
;
Tseng, YH
;
Shu, CF
;
應用化學系
We have synthesized a novel polyfluorene copolymer polyfluorene-bis[4-(diphenylamino)styryl]fluorene (PF-DPAS) by orthogonally attaching an amino-substituted distyrylarylene dye bis[4-(diphenylamino)styryl]fluorene, onto the C9 position of a fluorene unit. We have investigated this polymer's thermal properties, electronic properties (viz., absorption and photoluminescence), and electrochemical behavior. Photoluminescence studies indicate that color tuning can be achieved through efficient Forster energy transfer from the higher-energy polyfluorene backbone to the lower-energy pendant DPAS units. We have fabricated light-emitting diodes with the structure indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) (PEDOT)/ emitting layer/1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBI)/Mg:Ag. The devices, based on blends of PF-DPAS in polyfluorene-triphenylamine-oxadiazole (PF-TPA-OXD), exhibit significant improvements in device performance relative to that of the pure PF-TPA-OXD device; we attributed this improvement to both a red-shift of the electroluminescence (EL) spectra and an enhancement in quantum efficiency. At a blend ratio of 1:20, the EL spectrum is voltage-independent and stable, and exhibits the characteristic emission of a DPAS moiety: a peak at 461 nm and Commission Internationale de l'Eclairage (CIE) coordinates of (0.1.5, 0.18). The maximum external quantum efficiency is 2.08 % (2.87 cd A(-1)) at a bias of 9 V (86.1 mA cm(-2)) with a brightness of 2467 cd m(-2); the maximum brightness (6916 cd m-2) occurred at an applied voltage of 13 V and a current density of 361 mA cm(-2).
Polyfluorene containing diphenylquinoline pendants and their applications in organic light emitting diodes
(2005-02-15)
Su, HJ
;
Wu, FI
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Shu, CF
;
Tung, YL
;
Yun, C
We present a short, efficient synthetic route for the preparation of a novel polyfluorene copolymer (PF-Q) containing two electron-deficient, 2,4-diphenylquinoline groups functionalized at the C-9 positions of alternate fluorene units that form a three-dimensional cardostructure. The presence of the rigid bulky pendent groups leads to a polyfluorene possessing a high glass-transition temperature (207 degreesC) and very good thermal stability (5% weight loss observed at 460 degreesC). A photoluminescence study revealed that the Forster energy transfer from the excited quinoline groups to the polyfluorene backbone is Very efficient; it also demonstrated that, the commonly observed aggregate/excimer formation in polyfluorenes is suppressed very effectively, in this polymer, even after it has been annealed at 150 degreesC for 20 h. A light emitting diode (LED) device prepared with PF-Q as the emitting layer exhibits a stable blue emission with a maximum brightness of 1121 cd/m(2) at 12 V and a maximum external quantum efficiency of 0.80% at 250 cd/m(2). We also used PF-Q, which contains diphenylquinoline units that behave as electron-transporting side chains, as a host. material and doped it with 2.4 wt % of a red-emitting phosphorescent dye, Os(fppz). to realize a red electrolumineseence with CIE color coordinates of (0.66, 0.34). The doped device exhibits a maximum external quantum efficiency of 6.63% (corresponding a luminance efficiency of 8.71 cd/A) at a current density of 47.8 mV/cm(2) together with a maximum brightness of 10457 cd/m(2). (C) 2005 Wiley Periodicals, Inc.
Tuning the emission and morphology of cyclometalated iridium complexes and their applications to organic light-emitting diodes
(2005)
Wu, FI
;
Su, HJ
;
Shu, CF
;
Luo, LY
;
Diau, WG
We have synthesized two highly efficient phosphorescent iridium metal complexes, Ir( DPQ)(2)( acac) and Ir(FPQ)(2)(acac), which are based on cyclometalated quinoline ligands, and discuss details of their electrochemical behavior and photophysical properties (viz. absorption and photoluminescence). Single-crystal X-ray diffraction studies of Ir(DPQ)(2)(acac) reveal a distorted octahedral geometry, in which the quinoline N atoms and the C atoms of the orthometalated phenyl groups are located at mutual trans and cis positions, respectively. In contrast, Ir(FPQ)(2)( acac) is an amorphous solid and undergoes a glass transition at 92 degreesC, which we attribute to the presence of the long di-n-octyl chains in the fluorenyl groups. The phosphorescence of these Ir complexes originates from the dominant 3 MLCT excited state shifts to red that occur upon introducing a phenyl substituent and/or a large conjugating aromatic ring into the ligand. A polymer light-emitting diode (PLED) device that uses Ir(FPQ)(2)(acac) as a phosphorescent dopant and a PVK/PBD blend as the host material produces very high efficiency (an external quantum efficiency of 8.16% at 100 mA cm(-2)) and a pure-red emission with 1931 CIE ( Commission Internationale de L'Eclairage) chromaticity coordinates of (x = 0.68, y = 0.32).
Tuning wavelength: Synthesis and characterization of spiro-DPVF-containing polyfluorenes and applications in organic light-emitting diodes
(2004-09-21)
Su, HJ
;
Wu, FI
;
Shu, CF
;
應用化學系
;
Department of Applied Chemistry
We have synthesized polyfluorene copolymers containing bis(2,2-diphenylvinyl)fluorene pendent groups attached orthogonally to the C-9 positions of fluorene units. These polymers possess high glass transition temperatures and good thermal stability. The results from PL studies indicate that most excitons formed in the polyfluorene backbone by direct photoexcitation are likely to migrate to lower-energy pendent groups, from which emission occurs. An organic light-emitting device using the copolymer PF4-DPVF as the emitting layer exhibits a voltage-independent and stable blue emission with color coordinates (0.15, 0.17) at 11 V, with a maximum brightness of 3137 cd/m(2) at 9 V (262 mA/cm(2)) and a maximum external quantum efficiency of 1.06%. In addition, we blended PF4-DPVF as the host material with 0.5 wt % of MEH-PPV to realize a white electroluminescence having CIE coordinates of (0.29,0.34) and a maximum brightness of 3258 cd/m(2) (119 mA/cm(2)). We demonstrate that both Forster energy transfer and direct charge trapping/recombination on the MEH-PPV guest are responsible for the observed EL.