Browsing by Author "Chao, CS"

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Effect of side chain alkyl length on the electroluminescence characteristics of carbazole-based light emitting polymers
(2001-09-28)
Chao, CS
;
Whang, WT
;
Hung, CH
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Three carbazole-based copolymers with different long side chains were synthesized using the Wittig reaction. These three copolymers and model compound were characterized by nuclear magnetic resonance (NMR) spectroscopy to determine the cis/trans ratio. The cis/ trans ratios decrease with the side chain length due to the variation in the degree of steric hindrance in the Wittig reaction. They affect the electroluminescence (EL) characteristics of the carbazole-based light emitting polymers. As the length of the side chain increases the wavelength of the emitted light increases proportionally whereas a decrease in the threshold voltages, 5.2, 4.8, 2.5 V was observed. However, EL intensity at same applied voltage creases with the length of the side chain. The energy levels of these three copolymers were also investigated to account for the phenomenon.
Significant improvement on the electroluminescence characteristics of MEH-PPV by blending with PMMA
(2000-09-01)
Chao, CS
;
Whang, WT
;
Chuang, KR
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A significant improvement on the electroluminescence threshold voltage from 5.5 volts down to 2.9 volts of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) in the Ca/polymer/ITO diode is observed by incorporating a non-conjugated PMMA into MEH-PPV. The threshold voltage of the material decreases with the poly(methyl methacrylate) (PMMA) content. Near-field scanning absorption and photoluminescence micrographs show that the PMMA domains dispersed in the continuous MEH-PPV phase appear to be similar to sesame seeds embedded in the MEH-PPV pancakes. The resistivity of PMMA is two orders lower than that of MEH-PPV. The excellent electrical conduction of PMMA in Ca/PMMA/ITO glass devices is not due to a pin-hole defect mechanism but may result from the electron hopping from Ca through the carbonyl groups in the PMMA. The significant improvement in the threshold Voltage may be due to the combination of the electron hopping in the thin PMMA sesame seeds and the thinner thickness effect of MEH-PPV in the light emitting layer.
Synthesis of new type diacetal trioxa-cage compounds via an intramolecular nucleophilic addition of the hydroxy group to the carbonyl oxide group
(1998-10-30)
Wu, HJ
;
Chao, CS
;
Lin, CC
;
應用化學系
;
Department of Applied Chemistry
The synthesis of diacetal trioxa-cage compounds with a new type of skeleton is reported. Ozonolysis of the diols 2a-f, 21, 24, and 33 in CH2Cl2 at -78 degrees C followed by reduction with Me2S gave the diacetal trioxa-cages 3a-f, 22, 25, and 34 in 70-80% yields, respectively. A mechanism via an intramolecular nucleophilic addition of the hydroxy group of the diols to the carbonyl oxide group is proposed for the formation of the diacetal trioxa-cages. The effect of the number of carbon atoms at the bridge of the diols on the formation of the diacetal trioxa-cage skeleton was examined. Ozonolysis of the diols 13 and 15 under the same reaction conditions gave compounds 16 and 18, respectively. No detectable amount of the trioxa-cages 17 and 19 was obtained. For the synthesis of the diacetal trioxa-cages 28a-c and 31, which possess an alkene bond intact, ozonolysis of the diols 27a-c and 30 was performed by controlling the amount of ozone.
Synthesis of new type diacetal trioxa-cage compounds via an intramolecular nucleophilic addition of the hydroxy group to the carbonyl oxide group
(1998-10-30)
Wu, HJ
;
Chao, CS
;
Lin, CC
;
應用化學系
;
Department of Applied Chemistry
The synthesis of diacetal trioxa-cage compounds with a new type of skeleton is reported. Ozonolysis of the diols 2a-f, 21, 24, and 33 in CH2Cl2 at -78 degrees C followed by reduction with Me2S gave the diacetal trioxa-cages 3a-f, 22, 25, and 34 in 70-80% yields, respectively. A mechanism via an intramolecular nucleophilic addition of the hydroxy group of the diols to the carbonyl oxide group is proposed for the formation of the diacetal trioxa-cages. The effect of the number of carbon atoms at the bridge of the diols on the formation of the diacetal trioxa-cage skeleton was examined. Ozonolysis of the diols 13 and 15 under the same reaction conditions gave compounds 16 and 18, respectively. No detectable amount of the trioxa-cages 17 and 19 was obtained. For the synthesis of the diacetal trioxa-cages 28a-c and 31, which possess an alkene bond intact, ozonolysis of the diols 27a-c and 30 was performed by controlling the amount of ozone.