Browsing by Author "Sung, HH"

Now showing 1 - 4 of 4

Effect of polar substituents on the properties of 1,3,4-oxadiazole-based liquid crystalline materials containing asymmetric cores
(2004-06-01)
Sung, HH
;
Lin, HC
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A series of 1,3,4-oxadiazole-based liquid crystals bearing different polar substituents (n-NPO-X, where X = Me, OMe, Cl, F, CN, and NO2) at the phenyl 4-position have been synthesized and characterized. These angular oxadiazole-based liquid crystals, which are composed of asymmetric cores containing naphthalene units, exhibit stable mesogenic properties including the nematic and smectic A phases. With analogous structural design, the transition temperatures, mesomorphic phases, optical properties, and internal quantum efficiencies show strong dependence on the terminal substitution. In general, by increasing the terminal dipoles, the temperature ranges of the mesophases are enhanced, and both the absorption and photoluminescence spectra are shifted to longer wavelengths.
Novel alternating fluorene-based conjugated polymers containing oxadiazole pendants with various terminal groups
(2004-10-19)
Sung, HH
;
Lin, HC
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A series of soluble alternating fluorene-based copolymers containing symmetrical and asymmetrical 1,3,4-oxadiazole (OXD) pendants with various terminal groups are synthesized by the palladium-catalyzed Suzuki coupling reaction. These polymers possess higher glass transition temperatures than that of the analogous dialkoxy-substituted polymer (PFPOC6) consisting of the same backbone without OXD pendants. The photophysical and electrochemical properties of these polymers are affected by the polar effect (electron-withdrawing group, -CN, and electron-donating group, -R or -OR) and the size effect (the size of the grafted side chain) of the OXD pendants. Owing to the large steric hindrance of OXD pendants, the aggregation of these polymers in solids is reduced, which results in almost identical PL emissions in both solution and solid states. The bulky OXD pendants on the polymer side chains can provide the polymer films with lower HOMO and LUMO energy levels and better electron injection property. Since only one emission peak is observed in both PL and EL spectra of these polymers, it is evidenced that effective energy transfer from the OXD pendants to the conjugated polymer backbones has occurred, thus eliminating the light emission from the OXD pendants. These asymmetrical OXD-substituted polymers have higher quantum yields and less aggregation in the solid state than the symmetrical OXD-substituted polymers. The symmetrical OXD-substituted polymer (P1) has a longer PL emission wavelength than the asymmetrical OXD-substituted polymers (P2-P8), which may be due to the improvement of the coplanarity between the polymer backbone and the symmetrical OXD pendants and/or the introduction of two electron-withdrawing OXD pendants.
Synthesis and characterization of alternating fluorene-based copolymers containing diaryl- and non-substituted bithiophene units
(2005-11-14)
Lin, HC
;
Sung, HH
;
Tsai, CM
;
Li, KC
;
材料科學與工程學系
A series of soluble alternating fluorene-based copolymers containing diaryl- and non-substituted bithiophene units are synthesized by palladium-catalyzed Suzuki coupling reaction. All polymers demonstrate green colors of photoluminescence (PL) in chloroform, good thermal stability (with, decomposition temperatures above 436 degrees C), and high glass transition temperatures (in the range of 120-144 degrees C). Owing to the large steric hindrance of diaryl substituents on bithiophenes in the polymers (P2-P4), the aggregation of solids is reduced as well as the solubility is improved, so the performance of their PLED devices are superior to that of the non-substituted polymer (PI). Compared with P1, the introduction of substitutents at 3,3'-position of bithiophene in P2-P4 has significant effects on the photophysical properties of resulting polymers in solution and solid states. Though the PL quantum yield of P1 is much higher than those of diaryl-substituted polymers (P2-P4), the PLED device of P1 has the worst electroluminescence (EL) properties due to the poor solubility of P1. Consequently, among these polymers, the device made of P3 as an emitter has the highest luminance of 2590 cd/m(2) at 9.5 V. For optimum device performance, a device of P3 blended with PVK can be further enhanced to a brighter luminance of 4284 cd/m(2) at 18 V. (c) 2005 Elsevier Ltd. All rights reserved.
Synthesis and characterization of poly(fluorene)-based copolymers containing various 1,3,4-oxadiazole pendants
(2005-07-01)
Sung, HH
;
Lin, HC
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A series of soluble alternating poly(fluorene)-based copolymers containing electron-transporting 1,3,4-oxadiazole (OXD) and hole-transporting carbazole pendants attached to the C-9 position of fluorene units by long alkyl spacers were synthesized. These copolymers possess mesogenic and nomnesogenic pendants attached to a rigid mesogenic poly(fluorene) (PF) backbone. All these polymers exhibit glass-forming liquid crystalline properties, including the nematic and smectic A (SmA) phases, and reveal much wider mesophasic temperature ranges than that of PF. The thermal properties and mesomorphism of these conjugated polymers are mainly affected by the nature of these pendants, and thus the mesophasic temperature ranges and glass-forming properties are greatly enhanced by introducing the OXD pendants. In addition, the tendencies of crystallization and aggregation of PF are also suppressed by introducing the OXD pendants. A single layer device with P4 as an emitter shows a turn-on voltage of 5 V and a bright luminescence of 2694 cd/m(2) at 11 V with a 2 power efficiency of 1.28 cd/A at 100 mA/cm(2). (c) 2005 Wiley Periodicals, Inc.