Showing papers by "Kung-Hwa Wei published in 2007"

Soluble Phenanthrenyl-Imidazole-Presenting Regioregular Poly(3-octylthiophene) Copolymers Having Tunable Bandgaps for Solar Cell Applications†

Abstract: We have used Grignard metathesis polymerization to successfully synthesize a series of regioregular polythiophene copolymers that contain electron-withdrawing and conjugated phenanthrenyl-imidazole moieties as side chains. The introduction of the phenanthrenyl-imidazole moieties onto the side chains of the regioregular polythiophenes increased their conjugation lengths and thermal stabilities and altered their bandgap structures. The bandgap energies, determined from the onset of optical absorption, could be tuned from 1.89 eV to 1.77 eV by controlling the number of phenanthrenyl-imidazole moieties in the copolymers. Moreover, the observed quenching in the photoluminescence of these copolymers increases with the number of phenanthrenyl-imidazole moieties in the copolymers, owing to the fast deactivation of the excited state by the electron-transfer reaction. Both the lowered bandgap and fast charge transfer contribute to the much higher external quantum efficiency of the poly(3-octylthiophene)-side-chain-tethered phenanthrenyl-imidazole than that of pure poly(3-octylthiophene), leading to much higher short circuit current density. In particular, the short circuit current densities of the device containing the copolymer having 80 mol% phenanthrenyl-imidazole, P82, improved to 14.2 mAcm –2 from 8.7 mAcm –2 for the device of pure poly(3-octylthiophene), P00, an increase of 62%. In addition, the maximum power conversion efficiency improves to 2.80% for P82 from 1.22% for P00 (pure P3OT). Therefore, these results indicate that our polymers are promising polymer photovoltaic materials.

Studies of surface-modified gold nanowires inside living cells

Abstract: The cytotoxicity of various surface-functionalized gold nanowires with different aspect ratios is investigated by (3-(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide) (MTT) assays for two cell lines, fibroblast and HeLa. It is found that functionalized gold nanowires with a diameter of 200 nm and lengths up to a few micrometers can be readily internalized by both types of cells regardless of the type of surface functionalization. However, the cytotoxicity of the gold nanowires is observed to depend on their surface modification. Serum-coated gold nanowires are the least toxic, whereas more than 50 % of the cells are damaged in the presence of mercapto-acid-modified gold nanowires even at very low concentrations (103 nanowires mL–1). Nanowires with different aspect ratios exhibit the same cytotoxicity within limits of experimental error. However, the uptake efficiency is found to be higher for shorter nanowires as compared to their longer counterparts. Therefore, we conclude that internalized nanowires with high aspect ratios are more toxic to cells than nanowires with low aspect ratios. Positively charged aminothiol-modified gold nanowires are employed to deliver both plasmid DNA and probe molecules into cells without compromising the viability of the cells. The local environment of individual nanowires within the cells is studied by monitoring the fluorescence signal from probe molecules attached to the nanowires.

The Effect of Nanoscale Confinement on the Collective Electron Transport Behavior in Au Nanoparticles Self‐Assembled in a Nanostructured Polystyrene‐block‐poly(4‐vinylpyridine) Diblock Copolymer Ultra‐thin Film

Abstract: This study involves the collective electron transport behavior of sequestered Au nanoparticles in a nanostructured polystyreneblock-poly(4-vinylpyridine) The monolayer thin films (ca 30 nm) consisting of Au nanoparticles self-assembled in the 30-nm spherical poly(4-vinylpyridine) domains of an polystyrene-block-poly(4-vinylpyridine) diblock copolymer were prepared From the current-voltage characteristics of these thin films, the collective electron transport behavior of Au nanoparticles sequestered in the spherical poly(4-vinylpyridine) nanodomains was found to be dictated by Coulomb blockade and was quasi one-dimensional, as opposed to the three-dimensional behavior displayed by Au nanoparticles that had been dispersed randomly in homo-poly(4-vinylpyridine) The threshold voltage of these composite increased linearly upon increasing the inter-nanoparticle distance The electron tunneling rate constant in the case of Au nanoparticles confined in poly(4-vinylpyridine) nanodomains is eight times larger than that in the randomly distributed case and it increases upon increasing the amount of Au nanoparticles This phenomenon indicates that manipulating the spatial arrangement of metal nanoparticles by diblock copolymer can potentially create electronic devices with higher performance

Structural Evolution of Poly(styrene-b-4-vinylpyridine) Diblock Copolymer/Gold Nanoparticle Mixtures from Solution to Solid State

Abstract: We used in situ annealing small-angle X-ray scattering to monitor the structural evolution of a spherical poly(styrene-b-4-vinylpyridine) diblock copolymer (PS-b-P4VP)/2-phenylethanethiol-coated Au nano- particle (AuSC2Ph) mixture in the solid state during its thermal annealing. We found that the Au nanoparticles (NPs) that existed initially in a random state with some cluster packing in the PS domain diffused to the interface of the amphiphilic PS-b-P4VP diblock copolymer withi n4ha t 170°C under vacuum to form NP-filled shell- like assemblies, as further evidenced from transmission electron microscopy imaging. From the X-ray photoelectron spectroscopy data, we speculate that this interfacial activity of AuSC 2Ph results from the fact that the initially hydrophobic Au NP surfaces became increasingly hydrophilic as most of the 2-phenylethanethiol ligands had evaporated off. The Au NP nanoshell assemblies located at the interface between PS and P4VP were quite stable even after redissolving in toluene; they remained in the form of PS-Au-P4VP core/shell/corona onion micelles, as evidenced from solution state small-angle X-ray scattering data.

Dependence of the final-state effect on the coupling between a CdSe nanoparticle and its neighbors studied with photoemission spectroscopy

Abstract: A simple model based on an electrostatic calculation of the photoemission effect in the final state is used to characterize the energy shift, relative to bulk material, which is dependent on size in the photoemission spectra of organically passivated CdSe nanoparticles (NPs). For trioctylphosphine oxide/hexadecylamine-passivated NPs, the core-level shifts are well described with a model involving a static effect in the final state. After the NPs are treated with pyridine, the energy shifts are smaller; this decrease is ascribed to a dynamic effect in the final state describing a finite lifetime, on a femtosecond scale, of the photohole residing in the NP. This condition is intimately related to the coupling between the NP and metallic substrate and among NPs themselves. For the valence-band edge, an additional effect of the initial state due to quantum confinement is required to elucidate the energy shift. We find that this initial-state shift is smaller than a prediction according to a semiempirical pseudopotential calculation.

Blue electroluminescence enhancement of poly{2,7-(9,9′- dioctylfluorene)-co-4-diphenylamino-4′-bipenylmethylsulfide} incorporating side-chain-tethered gold nanoparticles

Abstract: Through in situ reduction of a gold precursor, we have tethered gold nanoparticles (Au NPs) to the side chains of poly{2,7-(9,9' -dioctylfluorene)-co-4-diphenylamino-4' -bipenylmethylsulfide) (PF-DBMS) through its ArSCH 3 anchor groups. The presence of 1 wt % of the tethered Au NPs led to a reduction in the degree of aggregation of the polymer chains, resulting in a 50 % increase in its quantum yield. The electroluminescence of a 1 wt % Au/PF-DBMS device was almost four times higher in terms of its maximum brightness and its full-width-at-half-maximum emission peak was much narrower than that of a pure PF-DBMS device; the presence of a small amount of Au NPs significantly enhances the electron injection and transport and suppresses the photo-oxidation of PF-DBMS.

Manufacturing method of polymer nanocomposite for light emitting diode

Abstract: PROBLEM TO BE SOLVED: To provide a manufacturing method of a polymer nanocomposite for a light emitting diode which improves efficiency in the electroluminescence and photo luminescence SOLUTION: Thiophenol-cadmium sulfide nanoparticles are obtained by modifying the surface of cadmium sulfide through a thiophenol surfactant, dendritic monomers are composed to be assembled with a monomer of diboron compound through a Suzuki coupling, a banding of the product of the composed monomers and the product of the polymerization are processed by a π-π interaction to obtain a copolyfluorene whose side chain is dendritic and whose chemical structure is PF-GX COPYRIGHT: (C)2007,JPO&INPIT