Browsing by Author "Tao, YT"

Now showing 1 - 5 of 5

Fluorene-based oxadiazoles: thermally stable electron-transporting materials for light-emitting devices
(2005-01-31)
Wu, FI
;
Shu, CF
;
Chien, CH
;
Tao, YT
;
應用化學系
We have synthesized and characterized a series of fluorene-based oxadiazole derivatives, in each of which two identical oxadiazole moieties are linked to a fluorene unit via an sp(3)-hybridized carbon atom (C-9) to form a rigid, nonplanar structure. This structural feature leads to a reduction in the tendency to crystallize and an increase in the glass transition temperature. Electrochemical studies revealed that these materials undergo reversible reductions and have high electron affinities. Each fluorene-based oxadiazole exhibited reasonably good performance when it was used as the electron-transporting layer in a multi-layer organic EL device. (C) 2004 Elsevier B.V. All rights reserved.
Spirobifluorene-based pyrazoloquinolines: efficient blue electroluminescent materials
(2004)
Chen, CH
;
Wu, FI
;
Shu, CF
;
Chien, CH
;
Tao, YT
We report the synthesis of spirobifluorene-based pyrazoloquinolines, spiro-PAQ-Me and spiro-PAQ-Ph, in which two identical luminophores are connected through an sp(3)-hybridized carbon atom (a spiro center) and are orthogonally arranged. The incorporation of the rigid spirobifluorene linkage results in significant increases in the glass transition temperatures, which are in the range 246-280degreesC. These new materials display the characteristic absorptions of the mono-pyrazoloquinoline (i.e. non-spiro) derivatives, each with a broad, low-energy absorption at ca. 420 nm, and emit photoluminescence efficiently in the blue region. Electrochemical studies reveal that these compounds exhibit reversible reductions and low-lying LUMO energy levels that originate from the electron-deficient nature of the pyrazoloquinoline ring. Multilayer organic electroluminescent devices constructed using spiro-PAQ-Ph as a dopant in the emitting layer produced bright blue emissions with maximum luminescence exceeding 20 000 cd m(-2). For the 2.0%-doped device, a high external quantum efficiency of 3.6% (4.5 cd A(-1), 2.02 lm W-1) was achieved at 20 mA cm(-2) and 7.0 V with color coordinates of (0.14, 0.17).
Synthesis and characterization of light-emitting H-bonded complexes and polymers containing bis(pyridyl) emitting acceptors
(2006-01-24)
Lin, HC
;
Tsai, CM
;
Huang, GH
;
Tao, YT
;
材料科學與工程學系
A series of bis(pyridyl) acceptor emitters are synthesized and the LC and photophysical (PL and EL) properties of their supramolecular structures, including H-bonded polymer networks and trimers, are explored. Unique mesomorphic properties may be introduced into these H-bonded complexes and polymers containing nonmesogenic acceptor emitters. In addition, the emission properties of bis(pyridyl) acceptor emitters can be adjusted by their surrounding nonphotoluminescent proton donors. Compared with pure bis(pyridyl) acceptor emitters, red-shifts of PL emission wavelengths were observed in most of the H-bonded complexes and polymers. Because of the higher acidity value of m-PC(10)BA (16) and its stronger H-bonded effect in H-bonded polymer complexes, the largest red-shift of 93 nm in lambda(max) value of PL has occurred in the fully H-bonded polymer network p-PBBBP-OC8 (8)/m-PC(10)BA (16) in contrast to pure emitter p-PBBBP-OC8 (8). A very narrow full width at half-maximum (fwhm) value (38 nm) of EL spectra can be obtained in the device of H-bonded complexes blended with PVK, and a higher brightness of EL is produced at an appropriate annealing temperature.
Synthesis and characterization of light-emitting oligo(p-phenylene-vinylene)s and polymeric derivatives containing three- and five-conjugated phenylene rings. II. Electro-optical properties and optimization of PLED performance
(2006-05-01)
Lin, HC
;
Tsai, CM
;
Tao, YT
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A series of multilayer polymeric light-emitting diodes (PLEDs) containing an electron-transporting layer (ETL), that is tris(8-quinolinolato)-aluminum(III) (Alq) and 2,2',2"-(1,3,5-phenylene)-tris[1-phenyl-1H-benzimidazole] (TPBI), were fabricated by doping fluorescent oligo(p-phenylene-vinylene)s (BIII and BV) and polymer derivatives (PBV) into poly(N-vinyl carbazole) (PVK). These PLEDs can be optimized by the design of multilayer device configurations (brightness increased 8-15 times by addition of ETL) and possess greenish electroluminescent (EL) spectra peaked about 500-540 nm. A remarkably high brightness of 56,935 cd/m(2) with a power efficiency of 3.25 lm/W was obtained in the device of PVK:BVOC8-OC8 (100:20)/Alq (60 nm/60 nm). It suggests that the emission mechanism (including the conjugated and excimer emissions of BVOC8-OC8 emitters) originates from both of BVOC8-OC8 and ETL (Alq and TPBI) by varying the concentration of chromophores and adjusting the thickness of ETL. The concentration effect of the emitters in PVK (i.e. PVK:BVOC8-OC8 = 100:5, 100:20, and 100:100 wt %) and the influence of the ETL (including its thickness) on the EL characteristics are also reported. (c) 2006 Wiley Periodicals, Inc.
White organic light-emitting diodes based on 2,7-bis(2,2-diphenylvinyl)-9,9 '-spirobifluorene: Improvement in operational lifetime
(2004-11-15)
Chuen, CH
;
Tao, YT
;
Wu, FI
;
Shu, CF
;
應用化學系
Very bright white organic light-emitting diodes were fabricated using 2,7-bis(2,2-diphenylvinyl)-9,9(')-spirobifluorene (DPVSBF) doped with [4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran)] (DCJTB) as the emission layer. With a device configuration of ITO/NPB(40 nm)/DPVSBF:0.2%DCJTB(11 nm)/Alq(30 nm)/LiF(1 nm)/Al(150 nm), a brightness of 1575 cd/m(2) with an external quantum efficiency of 3.31% and luminous efficiency of 8.00 cd/A, a power efficiency of 5.35 lm/W was achieved at a driving current of 20 mA/cm(2) (4.7 V). The brightness reached 66 000 cd/m(2) at 15 V. The Commission Internationale de l'Eclairage coordinates stayed nearly constant, changed from (0.35, 0.36) to (0.32, 0.34) when the voltage increased from 6 to 12 V. The relative operational lifetime of the device increased by a factor of similar to20 compared with a similar device based on 4,4(')-bis-(2,2-diphenylvinyl)-1,1(')-biphenyl as the source of the blue emission. The much extended half-lifetime was attributed to the higher morphological stability of the DPVSBF. (C) 2004 American Institute of Physics.