Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 11 de 11
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Nanoscale ; 11(44): 21196-21206, 2019 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-31663591

RESUMO

Semiconducting single-walled carbon nanotubes (s-SWCNTs) are attractive light-harvesting components for solar photoconversion schemes and architectures, and selective polymer extraction has emerged as a powerful route to obtain highly pure s-SWCNT samples for electronic applications. Here we demonstrate a novel method for producing electronically coupled thin films of near-monochiral s-SWCNTs without wrapping polymer. Detailed steady-state and transient optical studies on such samples provide new insights into the role of the wrapping polymer on controlling intra-bundle nanotube-nanotube interactions and exciton energy transfer within and between bundles. Complete removal of polymer from the networks results in rapid exciton trapping within nanotube bundles, limiting long-range exciton transport. The results suggest that intertube electronic coupling and associated exciton delocalization across multiple tubes can limit diffusive exciton transport. The complex relationship observed here between exciton delocalization, trapping, and long-range transport, helps to inform the design, preparation, and implementation of carbon nanotube networks as active elements for optical and electronic applications.

2.
Adv Mater ; 31(27): e1902250, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31074911

RESUMO

Doping of semiconductors enables fine control over the excess charge carriers, and thus the overall electronic properties, crucial to many technologies. Controlled doping in lead-halide perovskite semiconductors has thus far proven to be difficult. However, lower dimensional perovskites such as nanocrystals, with their high surface-area-to-volume ratio, are particularly well-suited for doping via ground-state molecular charge transfer. Here, the tunability of the electronic properties of perovskite nanocrystal arrays is detailed using physically adsorbed molecular dopants. Incorporation of the dopant molecules into electronically coupled CsPbI3 nanocrystal arrays is confirmed via infrared and photoelectron spectroscopies. Untreated CsPbI3 nanocrystal films are found to be slightly p-type with increasing conductivity achieved by incorporating the electron-accepting dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4 TCNQ) and decreasing conductivity for the electron-donating dopant benzyl viologen. Time-resolved spectroscopic measurements reveal the time scales of Auger-mediated recombination in the presence of excess electrons or holes. Microwave conductance and field-effect transistor measurements demonstrate that both the local and long-range hole mobility are improved by F4 TCNQ doping of the nanocrystal arrays. The improved hole mobility in photoexcited p-type arrays leads to a pronounced enhancement in phototransistors.

3.
J Phys Chem A ; 122(36): 7181-7201, 2018 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-30152691

RESUMO

Panchromatic absorbers that have robust photophysical properties enable new designs for molecular-based light-harvesting systems. Herein, we report experimental and theoretical studies of the spectral, redox, and excited-state properties of a series of perylene-monoimide-ethyne-porphyrin arrays wherein the number of perylene-monoimide units is stepped from one to four. In the arrays, a profound shift of absorption intensity from the strong violet-blue (B y and B x) bands of typical porphyrins into the green, red, and near-infrared (Q x and Q y) regions stems from mixing of chromophore and tetrapyrrole molecular orbitals (MOs), which gives multiplets of MOs having electron density spread over the entire array. This reduces the extensive mixing between porphyrin excited-state configurations and the transition-dipole addition and subtraction that normally leads to intense B and weak Q bands. Reduced configurational mixing derives from moderate effects of the ethyne and perylene on the MO energies and a more substantial effect of electron-density delocalization to reduce the configuration-interaction energy. Quantitative oscillator-strength analysis shows that porphyrin intensity is also shifted into the perylene-like green-region absorption and that the ethyne linkers lend absorption intensity. The reduced porphyrin configurational mixing also endows the S1 state with bacteriochlorin-like properties, including a 1-5 ns lifetime.

4.
J Phys Chem A ; 120(38): 7434-50, 2016 Sep 29.
Artigo em Inglês | MEDLINE | ID: mdl-27636001

RESUMO

Light-harvesting architectures that afford strong absorption across the near-ultraviolet to near-infrared region, namely, panchromatic absorptivity, are potentially valuable for capturing the broad spectral distribution of sunlight. One previously reported triad consisting of two perylene monoimides strongly coupled to a free base porphyrin via ethyne linkers (FbT) shows panchromatic absorption together with a porphyrin-like S1 excited state albeit at lower energy than that of a typical monomeric porphyrin. Here, two new porphyrin-bis(perylene) triads have been prepared wherein the porphyrin bears two pentafluorophenyl substituents. The porphyrin is in the free base (FbT-F) or zinc chelate (ZnT-F) forms. The zinc chelate (ZnT) of the original triad bearing nonfluorinated aryl rings also was prepared. The triads were characterized using static and time-resolved optical spectroscopy. The results were analyzed with the aid of molecular-orbital characteristics obtained using density functional theory calculations. Of the four triads, FbT is the most panchromatic in affording the most even distribution of absorption spectral intensity as well as exhibiting the largest wavelength span (380-750 nm). The triads exhibit fluorescence yields (0.35 for FbT-F in toluene) that are substantially greater than for the porphyrin benchmarks (0.049 for FbP-F). The singlet excited-state lifetimes (τS) for the triads in toluene decrease in the order FbT-F (2.7 ns) > FbT (2.0 ns) > ZnT (1.2 ns) ∼ ZnT-F (1.1 ns). The τS values in benzonitrile are FbT (1.3 ns) > FbT-F (1.2 ns) > ZnT-F (0.6 ns) > ZnT (0.2 ns). Thus, the free base triads exhibit relatively long (1.2-2.7 ns) excited-state lifetimes in both polar and nonpolar media. The combined photophysical characteristics indicate that FbT and FbT-F are the best choices for panchromatic light-harvesting systems. Collectively, the findings afford insights into the effects of electronic structure on the panchromatic behavior of ethynyl-linked porphyrin-perylene architectures that can help guide next-generation designs and utilization of these systems.

5.
J Phys Chem A ; 120(3): 379-95, 2016 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-26765839

RESUMO

Achieving tunable, intense near-infrared absorption in molecular architectures with properties suitable for solar light harvesting and biomedical studies is of fundamental interest. Herein, we report the photophysical, redox, and molecular-orbital characteristics of nine hydroporphyrin dyads and associated benchmark monomers that have been designed and synthesized to attain enhanced light harvesting. Each dyad contains two identical hydroporphyrins (chlorin or bacteriochlorin) connected by a linker (ethynyl or butadiynyl) at the macrocycle ß-pyrrole (3- or 13-) or meso (15-) positions. The strong electronic communication between constituent chromophores is indicated by the doubling of prominent absorption features, split redox waves, and paired linear combinations of frontier molecular orbitals. Relative to the benchmarks, the chlorin dyads in toluene show substantial bathochromic shifts of the long-wavelength absorption band (17-31 nm), modestly reduced singlet excited-state lifetimes (τS = 3.6-6.2 ns vs 8.8-12.3 ns), and increased fluorescence quantum yields (Φf = 0.37-0.57 vs 0.34-0.39). The bacteriochlorin dyads in toluene show significant bathochromic shifts (25-57 nm) and modestly reduced τS (1.6-3.4 ns vs 3.5-5.3 ns) and Φf (0.09-0.19 vs 0.17-0.21) values. The τS and Φf values for the bacteriochlorin dyads are reduced substantially (up to ∼20-fold) in benzonitrile. The quenching is due primarily to the increased S1 → S0 internal conversion that is likely induced by increased contribution of charge-resonance configurations to the S1 excited state in the polar medium. The fundamental insights gained into the physicochemical properties of the strongly coupled hydroporphyrin dyads may aid their utilization in solar-energy conversion and photomedicine.


Assuntos
Porfirinas/química , Espectrometria de Fluorescência
6.
Sci Rep ; 5: 9615, 2015 Apr 24.
Artigo em Inglês | MEDLINE | ID: mdl-25905989

RESUMO

The crystallinity of epitaxial graphene (EG) grown on a Hexagonal-SiC substrate is found to be enhanced greatly by capping the substrate with a molybdenum plate (Mo-plate) during vacuum annealing. The crystallinity enhancement of EG layer grown with Mo-plate capping is confirmed by the significant change of measured Raman spectra, compared to the spectra for no capping. Mo-plate capping is considered to induce heat accumulation on SiC surface by thermal radiation mirroring and raise Si partial pressure near surface by confining the sublimated Si atoms between SiC substrate and Mo-plate, which would be the essential contributors of crystallinity enhancement.

7.
J Nanosci Nanotechnol ; 15(11): 8508-14, 2015 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-26726543

RESUMO

As the development of manufacturing technology for electronic devices, propresses it is necessary to study manufacturing technologies for mass storage, low-volume, improved reliability, and low cost materials for electronic devices used in data communication. The noble metals are the most commonly used raw materials used in such manufacturing. However, the raw materials (Ag, Pt, etc.) are expensive and raise the manufacturing cost. So, there is a need to replace these materials with raw materials of low cost. Recently, the much-cheaper Cu has received attention in that it has the same properties as the noble metals. Cu has good physical and chemical properties. However, its anti-oxidation is weak. Therefore, to make up for this weak point, research has generally been conducted to find a method to coat copper with a noble metal. The coating, comprised of the noble metal, is strong against the oxidation of the Cu surface. In this study, we made Cu@Ag core-shell nanoparticles; these particles have the same level of electro-conductivity as Ag. These materials are expected to reduce the product cost of raw materials.

8.
J Org Chem ; 79(17): 7910-25, 2014 Sep 05.
Artigo em Inglês | MEDLINE | ID: mdl-25061710

RESUMO

We report the synthesis and basic photophysical characterization of strongly conjugated hydroporphyrin (chlorin and bacteriochlorin) dyads. Hydroporphyrins are connected at their respective 13 (ß) or 15 (meso) positions by ethynyl or butadiynyl linkers. Synthesis entails a series of palladium-catalyzed reactions, starting from appropriate bromobacteriochlorin or bromochlorin. Strong conjugation in the dyads results in a significant bathochromic shift of longest-wavelength (Qy-like) band, which in case of the 13-13' ethynyl-linked bacteriochlorin dyad is positioned past 800 nm. The Qy-like band is broad and split for the 13-13' linked chlorin and bacteriochlorin dyads. All dyads exhibit an intense, relatively narrow fluorescence emission band in nonpolar solvents. Bacteriochlorin dyads exhibit a strong dependence of fluorescence intensity on the solvent polarity, which results in more than 10-fold quenching of fluorescence in dimethylformamide. The assembling of hydroporphyrins into strongly conjugated arrays represents an efficient means to tune and expand their optical and photochemical properties, which should greatly broaden the properties attainable for these chromophores.

9.
J Colloid Interface Sci ; 365(1): 103-9, 2012 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-21993548

RESUMO

Copper nanoparticles are prepared in aqueous solution by reducing copper ions with hydrazine hydrate in the presence of cetyl trimethylammonium bromide (CTAB) and polyvinylpyrrolydone (PVP) as stabilizers. With only CTAB was used as stabilizer, copper nanoparticles are aggregated and partially oxidized to Cu(2)O. When both PVP and CTAB were used, dispersed copper nanoparticles with 56 nm diameter were obtained. Copper nanoparticles are simply mixed with poly (3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) in aqueous solution to form conducting composite. The effect of copper weight percent and surfactants on the conductivity and stability of the composite has been investigated.

10.
J Drug Target ; 17(1): 19-28, 2009 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-19016067

RESUMO

Interleukin-18 (IL-18) is known to reduce melanoma lung metastases through various mechanisms. For the delivery of IL-18 gene into the lung, three different cationic emulsions as non-viral vectors were formulated using the same components of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), 1,2-dioleoyl-sn-glycero-3-trimethylammonium propane (DOTAP), and Tween 80 with distinct oils. By using the small particle size of physicochemically stable E3, the complex of E3/plasmid DNA encoding IL-18 (16:2.5, w/w) was transfected into lung cancer cells, and the amount of plasmid DNA transferred and the expression of both mRNA and protein for IL-18 were measured. When compared with Lipofectamine/DNA complexes, an E3/DNA complex was less toxic and induced a comparable cellular level of plasmid DNA and expression levels of both mRNA and protein for IL-18. After injecting E3/DNA complexes into mice, the distribution of plasmid DNA was the highest in the lung and the liver. Especially, the administration of E3/DNA complexes induced a more rapid and prolonged distribution of plasmid DNA encoding IL-18 into the lung than that of Lipofectamine/DNA ones. These data demonstrated that cationic emulsion E3 containing castor oil could be useful for a delivery of IL-18 gene targeting the lung as well as the liver without an additional homing device, implying a potential IL-18 delivery system for the treatment of lung cancer.


Assuntos
Emulsões/administração & dosagem , Emulsões/química , Técnicas de Transferência de Genes , Interleucina-18/administração & dosagem , Interleucina-18/genética , Animais , Óleo de Rícino/química , Linhagem Celular Tumoral , DNA/administração & dosagem , DNA/química , DNA/genética , DNA/metabolismo , Adutos de DNA/administração & dosagem , Adutos de DNA/metabolismo , Estabilidade de Medicamentos , Emulsificantes/química , Ácidos Graxos Monoinsaturados/química , Injeções Intravenosas , Lipídeos/administração & dosagem , Camundongos , Camundongos Endogâmicos BALB C , Azeite de Oliva , Fosfatidiletanolaminas/química , Óleos Vegetais/química , Plasmídeos/administração & dosagem , Plasmídeos/química , Plasmídeos/genética , Plasmídeos/metabolismo , Polissorbatos/química , Compostos de Amônio Quaternário/química , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Óleo de Soja/química , Suínos
11.
Asian Spine J ; 1(1): 48-52, 2007 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-20411153

RESUMO

There have been paucity of reports on atlas hypoplasia, and as a result this condition is not clearly defined, nor well understood. The authors reported three cases of atlas hypoplasia that were found in adults who presented with myelopathic symptoms. On radiographic examination, it was found that the anterior-posterior diameter of the atlas was remarkably narrower in all three cases in comparison with normal persons. The MRI in all three cases also revealed intramedullary high signal lesions at the levels where severe spinal cord compression was present. This led to our diagnosis of atlas hypoplasia causing myelopathy.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA