Browsing by Author "Hsu, CS"

Now showing 1 - 20 of 81

Color-tunable multilayer light-emitting diodes based on conjugated polymers
(2004-02-16)
Huang, CC
;
Meng, HF
;
Ho, GK
;
Chen, CH
;
Hsu, CS
Wide-range low-voltage continuous color tuning is achieved in multilayer light-emitting diodes based exclusively on the commonly used high-efficiency electroluminescent conjugated polymers. There are three layers for red, green, and blue emission, and one extra layer for electron blocking. The color of the emitted photon depends on the position of the electron-hole recombination. Due to the stronger field dependence of the electron mobility relative to the hole mobility, the recombination zone is pushed away from the cathode and concentrated in different emissive layers as the voltage increases. (C) 2004 American Institute of Physics.
Dipping and photo-induced liquid crystal alignments using silane surfactants
(2000-02-01)
Liao, YJ
;
Hsu, CS
;
Wu, ST
;
應用化學系
;
Department of Applied Chemistry
Dipping and photo-induced liquid crystal (LC) alignments were demonstrated using new silanes as surface coupling agents. In the dipping method, both homogeneous and homeotropic alignments can be achieved depending on the alkyl chain length of the silane employed. The 110 degrees C post curing temperature makes the dipping method especially attractive for low temperature processing of active matrix displays. In the UV-induced LC alignment, homogeneous cells are obtained and the LC directors are perpendicular to the impinging UV polarization. The pretilt angle of both methods is found to be similar to 0.5 degrees.
Effect of a lateral substituent on the mesomorphic properties of ferroelectric side chain liquid crystalline polysiloxanes
(1997-06-01)
Hsu, CS
;
Tsai, CH
;
交大名義發表
;
應用化學系
;
National Chiao Tung University
The synthesis of side chain liquid crystalline polysiloxanes containing oligooxyethylene spacers and (S)-2-methylbutyl 4-[(4-oxybiphenyl-4'-yl)carbonyloxyl-3-fluorobenzoate mesogenic side groups is presented. Differential scanning calorimetry, optical polarizing microscopy and X-ray diffraction measurements reveal liquid crystalline properties for all synthesized monomers and polymers. All three precursor olefinic monomers reveal cholesteric and smectic A phases. The olefinic monomer which contains two oligooxyethylene units in the spacer is the only one which reveals a twist grain boundary A phase and a blue phase, besides the cholesteric and smectic A phases. All three polysiloxanes present enantiotropic smectic A and chiral smectic C phases. The mesomorphic behaviours of the monomers and polymers are compared with those of the corresponding monomers and polymers without the lateral fluoro substituent. The results seem to demonstrate that incorporating a lateral fluoro substituent in the mesogenic cores of the monomers affects not only the mesophase thermal stability, but also the nature of the mesophases formed. However, incorporating a lateral fluoro substituent in the mesogenic cores of the polymers affects only the thermal stability of the mesophases formed. The lateral fluoro substituent has a more profound effect on the mesomorphic behaviour for the monomers than that for the polymers.
Effect of a lateral substituent on the mesomorphic properties of ferroelectric side chain liquid crystalline polysiloxanes
(1997-06-01)
Hsu, CS
;
Tsai, CH
;
應用化學系
;
Department of Applied Chemistry
The synthesis of side chain liquid crystalline polysiloxanes containing oligooxyethylene spacers and (S)-2-methylbutyl 4-[(4-oxybiphenyl-4'-yl)carbonyloxyl-3-fluorobenzoate mesogenic side groups is presented. Differential scanning calorimetry, optical polarizing microscopy and X-ray diffraction measurements reveal liquid crystalline properties for all synthesized monomers and polymers. All three precursor olefinic monomers reveal cholesteric and smectic A phases. The olefinic monomer which contains two oligooxyethylene units in the spacer is the only one which reveals a twist grain boundary A phase and a blue phase, besides the cholesteric and smectic A phases. All three polysiloxanes present enantiotropic smectic A and chiral smectic C phases. The mesomorphic behaviours of the monomers and polymers are compared with those of the corresponding monomers and polymers without the lateral fluoro substituent. The results seem to demonstrate that incorporating a lateral fluoro substituent in the mesogenic cores of the monomers affects not only the mesophase thermal stability, but also the nature of the mesophases formed. However, incorporating a lateral fluoro substituent in the mesogenic cores of the polymers affects only the thermal stability of the mesophases formed. The lateral fluoro substituent has a more profound effect on the mesomorphic behaviour for the monomers than that for the polymers.
Effect of enantiomeric excess on surface structures and phase sequences in free-standing liquid-crystal films
(2002-12-01)
Cady, A
;
Liu, ZQ
;
Han, XF
;
Wang, ST
;
Veum, M
We present differential optical reflectivity and null transmission ellipsometry data from several mixtures of MHPBC enantiomers. From this data, we have determined the chiral smectic phase sequence as a function of enantiomeric excess. The data suggest a change in the structure of the smectic-C(alpha)* phase and the surface tilt state as the enantiomeric excess is reduced. The results also show that the intermediate phases, smectic C(FI2)*, smectic C(FI1)*, and smectic C(alpha)*, disappear sequentially on reducing the net chirality.
Effect of lateral substituent on the mesomorphic properties of ferroelectric side-chain liquid crystalline polysiloxanes.
(1996-08-25)
Hsu, CS
;
Tsai, CT
;
應用化學系
;
Department of Applied Chemistry
Effect of lateral substituent on the mesomorphic properties of ferroelectric side-chain liquid crystalline polysiloxanes.
(1996-08-25)
Hsu, CS
;
Tsai, CT
;
應用化學系
;
Department of Applied Chemistry
Effect of lateral substituents on the mesomorphic properties of side-chain liquid crystalline polysiloxanes containing 4-[(S)-2-methyl-1-butoxy]phenyl 4-(alkenyloxy)benzoate side groups
(1997-09-30)
Hsu, CS
;
Chu, PH
;
Chang, HL
;
Hsieh, TH
;
交大名義發表
The synthesis of side-chain liquid crystalline polysiloxanes containing either 4-[(S)-2-methyl-1-butoxy] phenyl 4-(alkenyloxy)benzoate or laterally fluoro-, chloro-, bromo-, and methoxy-substituted 4-[(S)-2-methyl-1-butoxy] phenyl 4-(alkenyl oxy)benzoate mesogenic side groups is presented. The mesomorphic properties of the synthesized polymers have been characterized by optical polarizing microscopy, differential scanning calorimetry, and X-ray diffraction measurements. The effects of spacer length and lateral substituent on the mesomorphic properties of the obtained polymers are examined. The five polymers which contain three methylene units in the spacers show no mesophase, while the five polymers which contain eleven methylene units in the spacer display smectic mesomorphism. Among the other fifteen polymers which contain respectively four, five, or six methylene units in the spacers, those with small fluoro and chloro substituents reveal respectively an Sd phase, while those with bulky bromo and methoxy substituents show no liquid crystalline behavior. The experimental results demonstrate that introducing a bulky lateral substituent into the mesogenic core of a polymer depresses the tendency to form a mesophase. Furthermore, the technique of thermally stimulated current has been used to study the dipolar relaxation mechanisms in a side-chain liquid crystalline polysiloxane. (C) 1997 John Wiley & Sons Inc.
Effect of lateral substituents on the mesomorphic properties of side-chain liquid crystalline polysiloxanes containing 4-[(S)-2-methyl-1-butoxy]phenyl 4-(alkenyloxy)benzoate side groups
(1997-09-30)
Hsu, CS
;
Chu, PH
;
Chang, HL
;
Hsieh, TH
;
應用化學系
The synthesis of side-chain liquid crystalline polysiloxanes containing either 4-[(S)-2-methyl-1-butoxy] phenyl 4-(alkenyloxy)benzoate or laterally fluoro-, chloro-, bromo-, and methoxy-substituted 4-[(S)-2-methyl-1-butoxy] phenyl 4-(alkenyl oxy)benzoate mesogenic side groups is presented. The mesomorphic properties of the synthesized polymers have been characterized by optical polarizing microscopy, differential scanning calorimetry, and X-ray diffraction measurements. The effects of spacer length and lateral substituent on the mesomorphic properties of the obtained polymers are examined. The five polymers which contain three methylene units in the spacers show no mesophase, while the five polymers which contain eleven methylene units in the spacer display smectic mesomorphism. Among the other fifteen polymers which contain respectively four, five, or six methylene units in the spacers, those with small fluoro and chloro substituents reveal respectively an Sd phase, while those with bulky bromo and methoxy substituents show no liquid crystalline behavior. The experimental results demonstrate that introducing a bulky lateral substituent into the mesogenic core of a polymer depresses the tendency to form a mesophase. Furthermore, the technique of thermally stimulated current has been used to study the dipolar relaxation mechanisms in a side-chain liquid crystalline polysiloxane. (C) 1997 John Wiley & Sons Inc.
Efficient white light emission in conjugated polymer homojunctions
(2004-11-15)
Ho, GK
;
Meng, HF
;
Lin, SC
;
Horng, SF
;
Hsu, CS
We study polymer light-emitting diodes with a homojunction, i.e., junction between two layers with the same host material. One layer is poly (9,9-dioctylfluorene-2,7-diyl) (PFO) host blended with a small amount of poly (2-methoxy-5 (2'-ethyl-hexyloxy)-1,4-phenylene vinylene), another layer is either pure PFO or PFO host blended with green-emitting polyfluorene copolymers. Such homojunction devices are solution processed and show efficient white light emission. The peak luminance 3000 cd/m(2) is reached at 10 V with Internationale de L'Eclairage (CIE) coordinate (0.34, 0.34). (C) 2004 American Institute of Physics.
Emission enhancement by formation of aggregates in hybrid chromophoric surfactant amphiphile/silica nanocomposites
(2006)
Bhongale, CJ
;
Hsu, CS
;
應用化學系
;
Department of Applied Chemistry
Enhancing the thermal and spectral stabilities of polyfluorene-based bluelight-emitting materials by incorporating pendent spiro-cycloalkyl groups
(2004-05-20)
Wu, FI
;
Dodda, R
;
Jakka, K
;
Huang, JH
;
Hsu, CS
We have synthesized polyfluorene-based copolymers containing spiro-cycloalkyl groups functionalized on the C-9 position of alternate fluorene units using the Suzuki coupling reaction. The presence of the rigid spiro-cycloalkyl pendent groups not only hinders the close packing and intermolecular interactions between polymer chains, but also preserves the molecular rigidity of the polymer, leading to polyfluorenes with high glass transition temperatures and improved thermal and spectral stabilities. The results of photoluminescence measurements of the isothermally heated spiro-polyfluorene thin films (150degreesC for 20h) show that the commonly observed aggregate/excimer formation is suppressed effectively in these polymers. Blue electroluminescence was demonstrated in a double-layer LED device using the spiro-derivatized polyfluorene as the emitting layer. (C) 2004 Elsevier Ltd. All rights reserved.
Fluorescent conjugated polymer films as TNT chemosensors
(2004-08-13)
Chang, CP
;
Chao, CY
;
Huang, JH
;
Li, AK
;
Hsu, CS
Three prototypical light emitting conjugated polymers, two poly(p-phenylene vinylenes) (MEH-PPV and DP10-PPV) and a poly(diphenylacetylene), were examined for chemosensor applications to detect explosive compounds such as 2,4,6-trinitrotoluene (TNT) and 2,4- and 2,6-dinitrotoluene (DNTs). All polymer thin films showed high fluorescence quenching sensitivity towards TNT and DNTs, indicating that a wide range of emissive conjugated polymers are potentially useful chemosensor materials for detecting landmines. The relative sensitivity of fluorescence quenching of the polymers by the analytes has been rationalized in terms of the vapor pressure of the analytes, the solubility parameters of the polymers and the analytes, and the relative energy levels of the polymers. (C) 2004 Elsevier B.V. All rights reserved.
Formation of nanostructures of hexaphenylsilole with enhanced color-tunable emissions
(2006-02-26)
Bhongale, CJ
;
Chang, CW
;
Diau, EWG
;
Hsu, CS
;
Dong, YQ
Nanostructures of 1,1,2,3,4,5-hexaphenylsilole (HPS) of various types were obtained on simple reprecipitation with THF as solvent and water as non-solvent. The formation and evolution of these nanostructures were monitored with scanning electron microscopy. Using picosecond time-correlated single-photon counting, we observed enhanced emission and fluorescence lifetimes at volume fractions 70-90% of added water. We report the first enhanced color-tunable emissions of a conjugated organic compound (HPS) due to the formation of nanoflowers, nanoglobules and microglobules, and provide time scales for those nanostructures and the corresponding intermolecular interactions in the aggregates. (c) 2005 Elsevier B.V. All rights reserved.
General method to solution-process multilayer polymer light-emitting diodes
(2006-04-17)
Tseng, SR
;
Lin, SC
;
Meng, HF
;
Liao, HH
;
Yeh, CH
An intermediate liquid buffer layer is introduced to overcome the dissolution problem of solution-processed multilayer conjugated polymer light-emitting diodes. This method can be applied to arbitrary combinations of polymers with no restriction on solvents. As an example, a hole-blocking layer is successfully spin coated on the common p-type emissive polymer layers. One green- and two blue-emitting polymers are chosen as the emissive layers. The electron-hole balance and efficiency are significantly improved by the addition of hole-blocking layer. The electroluminescence efficiency can be increased up to nine times, while the luminance up to seven times. In particular, 1.5 cd/A is obtained for deep blue emission from poly(9,9-dioctyl-fluorene) with 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene spin coated as the hole-blocking material. (c) 2006 American Institute of Physics.
High birefringence and wide nematic range bis-tolane liquid crystals
(1999-01-18)
Wu, ST
;
Hsu, CS
;
Shyu, KF
;
應用化學系
;
Department of Applied Chemistry
Several dialkyl and fluoro bis-tolane liquid crystals were synthesized and their physical properties evaluated. These highly conjugated liquid crystals exhibit a wide nematic range, small heat fusion enthalpy, high birefringence, and relatively low viscosity. Their excellent compatibility with commercial cyano mixtures makes these liquid crystals attractive for many electro-optic applications. (C) 1999 American Institute of Physics. [S0003-6951(99)02103-8].
High birefringent bistolane liquid crystals for LCD application
(1999)
Hsu, CS
;
Shyu, KF
;
Chuang, YY
;
Wu, ST
;
應用化學系
Several series of bistolane liquid crystals were synthesized and characterized. The structure-properties relationship of the obtained compounds is discussed. These highly conjugated liquid crystals exhibit not only high birefringence but also low melting temperature. Their potential applications for Rat panel display employing light scattering on Bragg reflection are emphasized.
High birefringent liquid crystals
(1995)
Wu, ST
;
Margerum, JD
;
Ho, MS
;
Fung, BM
;
Hsu, CS
Several liquid crystal dyes and fluorinated compounds with high birefringence are synthesized and their properties evaluated. These polar compounds are useful dopants for enhancing the dielectric anisotropy of the dialkyl diphenyl-diacetylene host.
Induced twisting in the self-assembly of chiral Schiff-based rod-coil amphiphiles
(2006-01-24)
Sung, CH
;
Kung, LR
;
Hsu, CS
;
Lin, TF
;
Ho, RM
A series of novel organic superstructures exhibiting diverse aggregate morphologies with liquid-crystalline-like properties were prepared by a simple precipitation method. Here, a chiral sugar moiety was simply introduced at the Schiff-based rod end of rod-coil molecules. In contrast to coil-coil molecules, the self-assembled rod-coil molecules exhibit a high segregation strength for phase separation because of their liquid-crystalline-like behavior. The morphological transformation of self-assembled chiral Schiff-based rod-coil amphiphiles, from a platelet-like morphology to helical twists, was obtained by increasing the length of the hydrophobic tail. Consistent with theoretical predictions, the bending force from the chiral entity depends on the size of the adjacent hydrophobic tail. That is, the size of hydrophobic chain determines the threshold of bending for the formation of a helical morphology. Moreover, by introducing an additional tethered hydrophobic chain self-assembled spherical vesicles can be obtained through the collapse of the twisted shape.
Liquid crystal alignment with a photo-crosslinkable and solvent-soluble polyimide film
(2000-05-15)
Lee, WC
;
Hsu, CS
;
Wu, ST
;
應用化學系
;
Department of Applied Chemistry
A new photo-crosslinkable and solvent-soluble polyimide containing cinnamate side chains (PICA) was developed for aligning nematic liquid crystals (LCs). Good LC alignment was achieved by exposing a long-wave linearly polarized ultraviolet (LPUV) light to the PICA film. The LC alignment direction is found perpendicular to the polarization axis of the incident LPUV light. The uniform alignment of LC molecules induced by PICA Films remains intact after being heated at 85 degreesC for 450 hours. A small pretilt angle on the PICA film was generated by the double exposure method.