Browsing by Author "Yang, SH"

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New soluble poly(2,3-diphenylphenylene vinylene) derivatives for light-emitting diodes
(2005-04-22)
Yang, SH
;
Chen, JT
;
Li, AK
;
Huang, CH
;
Chen, KB
Soluble poly(2,3-diphenylphenylene vinylene) (DP-PPV) derivatives, poly(2,3-diphenyl-5-(4-heptyloxy-4'-oxytrimethylenediphenyl)phenylene vinylene) (P1), poly(2,3-diphenyl-5-[4-(4-pentylcyclohexyl)phenoxyl-propyl-p-phenylene vinylene) (P2) and poly(2,3-diphenyl-5-(2-(1, 4, 5-triphenyl-1H-2-imidazoloyl)-1-oxytrimethylene phenyl) phenylene vinylene) (P3), were synthesized. P1 and P2 contain liquid crystal side groups; while P3 contains a charge transport group. The polymers showed solid state UV-Visible absorption and photoluminescence in the range of 370-380 and 480-510 nm, corresponding to blue green emission. Similar to many other reported systems, the solution fluorescence spectra of P1 and P2 showed slight solvent dependency and blue-shifted with respect to those of the films. These were not the case for P3 which showed little solvent dependency and little blue shift in solution. Two-layer light-emitting devices with a simple ITO/PEDOT/polymer/Ca (Al) configuration were fabricated and characterized. (c) 2004 Elsevier B.V. All rights reserved.
Novel poly(2,3-biphenyl-1,4-phenylenevinylene) derivatives containing long branched alkoxy and fluorenyl substituents: Synthesis, characterization, and their applications for polymer light-emitting diodes
(2005-10-18)
Chen, KB
;
Li, HC
;
Chen, CK
;
Yang, SH
;
Hsieh, BR
Two series of poly(2,3-Biphenyl-1,4-phenylenevinylene) (DP-PPV) derivatives containing long branched alkoxy chains or fluorenyl substituents were synthesized. The branched alkoxy groups were introduced to enhance the solubility for spin-coating processes. Bulky fluorenyl groups with two hexyl chains on the 9-position were introduced to increase steric hindrance and prevent close packing of the main chain. By controlling the feed ratio of different monomers during polymerization, DP-PPV derivatives with high molecular weights were obtained. All synthesized polymers possess high glass transitions temperatures and thermal stabilities. The maximum photoluminescent emissions of the thin films are located between 498 and 564 nm. Cyclic voltammetric analysis reveals that the band gaps of these light-emitting materials are in the range from 2.4 to 2.5 eV. A double-layer electroluminescent device with the configuration of ITO/PEDOT/polymer 2/Ca/Al exhibited a low turn-on voltage (4.0 V), a very high external quantum efficiency (3.39 cd/A), and a high brightness (16 910 cd/m(2)).
Optical and electrical investigations of poly(p-phenylene vinylene)/silicon oxide and poly(p-phenylene vinylene)/titanium oxide nanocomposites
(2005-01-03)
Yang, SH
;
Nguyen, TP
;
Le Rendu, P
;
Hsu, CS
;
應用化學系
Composites made by incorporation of silicon oxide (SiO2) or titanium (TiO2) nanoparticles into poly(p-phenylene vinylene) (PPV) have been fabricated and their electrical and optical properties have been investigated. The UV-vis absorption and Raman spectra showed that SiO2 nanoparticles reduced the conjugation lengths of PPV chains, while TiO2 nanoparticles did not. In the case Of SiO2 nanoparticles, the reduction of conjugation length was more noticeable on increasing the oxide concentration or on decreasing the particle size. Fourier transform infrared (FT-IR) spectra showed that both types of nanoparticles also reduced the formation of carbonyl groups in PPV main chains. Current-voltage characteristics measured in the indium tin oxide (ITO)-composite-MgAg diodes exhibit different electrical behavior to the composites depending on the particle size and the nature of the used oxide. The composite-electrode contact morphology, the polymer-dielectric particle contact, and the change in the polymer chain length are the possible explanations for these changes in behavior of the diodes. (C) 2004 Elsevier B.V. All rights reserved.
Optical and electrical properties Of PPV/SiO2 and PPV/TiO2 composite materials
(2005)
Yang, SH
;
Nguyen, TP
;
Le Rendu, P
;
Hsu, CS
;
應用化學系
Composites made by incorporation of SiO2 or TiO2 nanoparticles into poly (p-phenylene vinylene) (PPV) have been fabricated and their optical and electrical properties have been investigated. The UV-vis absorption band of the composite films showed a large blue-shift with SiO2 nanoparticles, but only little difference with TiO2 nanoparticles. Photoluminescence (PL) spectra showed the same blue-shift trend for SiO2 composites, and in addition, an increase in intensity of the high energy shoulder (515 nm) when the concentration of nanoparticles increased. Raman spectra showed a reduction of the 1547/1625 cm(-1) band ratio in SiO2 composites but not in TiO2 ones. These results suggest that SiO2 nanoparticles reduced the PPV conjugation length, while TiO2 nanoparticles did not. For SiO2 particles, the reduction of conjugation lengths is more pronounced on increasing the oxide concentration or on decreasing the particle size. Fourier-transform Infrared (FT-IR) spectra showed that both types of nanoparticles reduced the formation of carbonyl groups in PPV main chains. Current-voltage characteristics measured in ITO-composite-MgAg diodes exhibit different electrical behavior of the composites depending on the particle size and the nature of the oxide. The composite-electrode contact morphology, the polymer-dielectric particle contact and the change in the polymer chain length are the possible explanations for these changes in behavior of the diodes. (c) 2004 Published by Elsevier Ltd.
Optical properties of nanosize aggregation of phenylene vinylene oligomers
(2005-08-15)
Nguyen, TP
;
Yang, SH
;
Gomes, J
;
Wong, MS
;
應用化學系
In this paper, we report the experimental results on the optical properties of oligo-phenylene vinylenes (OPVs) formed in nanosize pores of porous silicon substrates. Strong modifications of the photoluminescence properties of nanosize aggregation of OPVs were observed at room temperature, such as a blue shift of the PL spectra, whereas the structure of the oligomers is preserved as proved by Raman scattering experiments. However, the penetration of the oligomers into the nanopores was found to depend on the conformation of the chains, which is, in turn, conditioned by the solvents, used to dissolve the oligomer powder. (C) 2005 Published by Elsevier B.V.
Optical properties of poly(2-methoxy-5-(2 '-ethyl-hexyloxy)-phenylene vinylene) deposited on porous alumina substrates
(2005)
Nguyen, TP
;
Yang, SH
;
Le Rendu, P
;
Khan, H
;
應用化學系
Thin films of poly(2-methoxy-5-(2'-ethyl-hexyloxy)-phenylene vinylene) (MEH-PPV) were deposited from solutions prepared with different solvents, on alumina-1%Mg substrates with different pore sizes from 18 to 118 nm to study the effects of the size on the optical properties of the polymer. The photoluminescence (PL) spectra of films cast from solutions using chloroform, toluene or xylene are almost similar, suggesting that the solvents have little effect on the solid films. In the composite systems, a blue shift of the polymer PL spectra was observed when the pore size decreases. Raman spectra recorded on these samples did not show significant changes compared to that of the polymer, suggesting that the structure of the polymer was preserved. The modifications observed in the PL spectra are attributed to the nanosize effect of the polymer deposited in the pores resulted from the chain conformation, which depends on the nature of the solvents used. (c) 2004 Elsevier Ltd. All rights reserved.
Synthesis and light emitting properties of polyacetylenes having pendent fluorene groups
(2006-01-01)
Huang, CH
;
Yang, SH
;
Chen, KB
;
Hsu, CS
;
應用化學系
Five novel fluorene-containing polymers, poly[(9,9-dimethylfluoren-2-yl)acetylenel (PFA1), poly[(1-pentyl-2-(9,9-dimethylfluoren-2-yl)acetylene) (PFA2), poly[1-decyl-2-(9,9-dimethylfluoren-2-yl)acetylene] (PFA3), poly[1-phenyl-2-(9,9-dimethylfluoren-2-yl)acetylenel (PFA4), and poly[1-(3,4-difluorophenyl)-2-(9,9-dimethylfluoren-2yl)acetylene] (PFA5) were synthesized by the polymerization of the corresponding fluorene-substituted acetylenic monomers (M1-M5), using WCl6, MoCl5, and TaCl5 as catalysts and n-Bu4Sn as a cocatalyst. The synthesized polymers were thermally stable and readily soluble in common organic solvents. The degradation temperatures for a 5% weight loss of the polymers were similar to 352-503 degrees C under nitrogen. PFA1-PFA5 show emission peaks from 402 to 590 nm. Besides, their electroluminescent properties were studied in heterostructure light-emitting diodes (LEDs), using PFA2-PFA5 as an emitting layer. The PFA5 device revealed an orange-red emission peak at 602 nm with a maximum luminescence of 923 cd/m(2) at 8 V. A device with the ITO/PEDOT/ a mixture of PFA2 (98 wt %) and PFA5 (2 wt %)/Ca/Al showed near white emission. Its maximum luminance and current efficiency are 450 cd/m(2) at 15 V and 1.3 cd/A, respectively. 0 2005 Wiley Periodicals, Inc.
Synthesis and opto-electrical properties of stellar polyfluorene derivatives containing polyhedral oligomeric silsesquioxanes as the center core
(2006-06-01)
Chen, KB
;
Chen, HY
;
Yang, SH
;
Hsu, CS
;
應用化學系
Three polyfluorene derivatives (P1-P3) emitting blue, green and red light were prepared via a Suzuki coupling method. Polyhedral oligomeric silsesquioxanes (POSS) were integrated into the center core of the derivatives to create stellar light-emitting polymers (POSS-P1-POSS-P3). The glass-transition and decomposition temperatures were raised after introducing POSS moieties. The starlike polymers showed a reduced emissive band at 540 nm when annealing at 200 degrees C. The result implies that integrated POSS at the center core suppresses the keto effect generally occurring for polyfluorenes. Double-layer light-emitting devices of indium tin oxide/poly(ethylenedioxythiophene)/polymer/Ca/Al were fabricated to evaluate polymer potential. Compared with pristine polymers, the maximum brightness and the current efficiency of devices using POSS-containing polymers as active layers were enhanced. A blending method using P1 or POSS-P1 as the host matrix further improved device performance.