Search

Initial experiments using differentially functionalized fullerenes, CD-C60, hexa-C60, and tris-C60, suggested a properties dependent effect on cytotoxic and proliferative responses in human skin keratinocytes. In the present study we investigated the cytokine secretion profile of dermal epithelial cells exposed to functionalized fullerenes. Keratinocyte-derived cytokines affect homing and trafficking of normal and malignant epidermal immune as well as nonimmune cells in vivo. These cytokines are critical for regulating activation, proliferation, and differentiation of epidermal cells. Our results indicate that tris-C60 (size range <100 nm) significantly reduces inflammatory cytokine release in a dose- and time-dependent manner. In contrast CD-C60 demonstrated a relatively pro-inflammatory cytokine response, while hexa-C60 did not significantly perturb cytokine responses. Physical and chemical characterizations of these engineered nanomaterials suggest that the disparate biological responses observed may potentially be a function of the aggregation properties of these fullerenes. [ABSTRACT FROM AUTHOR]

Abstract: Engineered fullerenes are widely integrated into several commercial and medical products and are now also being recognized as byproducts of many industrial activities. For most applications fullerenes have to be chemically modified. Surface modification of fullerenes can potentially impact their effect on biosystems. The purpose of the current study was to establish criteria to correlate fullerene structure to biological responses. We report studies of cellular responses induced by three different types of fullerenes that provide varying chemical and physical properties such as electronic behavior, solubility, and degree of agglomeration. Using a systematic and multipronged approach for material characterization and employing critical biological endpoints, we determined the impact of the physicochemical properties of fullerenes on cellular interactions. We examined the ability of these fullerenes to regulate intracellular oxidative stress, necrosis and apoptosis in human monocytic THP1 cells. Results indicate that the carboxylate derivatization of fullerenes was the determining factor in their ability to induce apoptosis. In contrast, the dispersion characteristics of fullerenes were found to be more relevant when considering their redox function. We also established a significant role for functionalization-dependent fullerene-regulation of the caspase proteases in the elicited responses. In addition, there was a notable increase in the level of several anti-oxidant enzymes. Collectively, the results clearly indicate that the physicochemical properties of fullerenes significantly influence the elicited biological response, thus impacting future applications. This study is an initial effort to lay the groundwork for routine correlation and predictive analysis on engineered fullerenes, thus expediting their use. [Copyright &y& Elsevier]

We report chemical deposition of metal particles and clusters with various sizes and morphologies on top of the polyaniline (PANI) thin films and porous asymmetry membranes. Immersing the PANI membrane into the PtCl42-gives rise to 3−5 nm Pt nanoparticles spread evenly on the membrane surface, while immersing undoped PANI membrane into AgNO3aqueous solution leads to the formation of micrometer size Ag sheets with strong anisotropy. In contrast to the Ag deposited on the undoped PANI membrane, Ag metal deposited on the doped PANI membrane has a random morphology and shows no preferential growth along a specific crystallographic direction. The Au metal deposited on the undoped and doped PANI membranes exhibit morphological differences from a sheetlike structure to larger particles comprised of smaller Au particulates (rice-grain shape). Furthermore, by varying the nature of the dopant, we can achieve deposition of metal structures with fiber, sheet, cube, yarn-ball, and leaf-like morphologies. Our studies demonstrate that tunable metal size and morphology can be easily achieved through tailoring the surface chemistry of conducting polymer by varying the dopant, oxidation state (doped and undoped), and polymer chain orientation. Our future goal is to further enhance the control over metal structure and morphology using a simple chemical deposition method. [ABSTRACT FROM AUTHOR]

This article reports a novel approach to synthesize chiral polyaniline (PANI) nanofibers in an aqueous solution. This new approach requires the following conditions: Polymerization was carried out in concentrated camphor sulfonic acid solutions; Aniline oligomers were used to accelerate the polymerization reaction. Ammonium persulfate was added incrementally to the aniline solution. An optimized procedure for the synthesis of chiral, nanostructured PANI carried out at 25 °C leads to the formation of a dark-green viscous suspension in 2h after all of the ammonium persulfate was added.

DNA sequence-dependent photoluminescence enhancement is found for a cationic polyelectrolyte complexed with single stranded DNA and described as a result of an interplay between electrostatic attraction and the π-π stacking between the polyelectrolyte's backbone and DNA's bases. [ABSTRACT FROM AUTHOR]

This review summarizes the most widely used mechanisms in memory devices based on conjugated polymers, such as charge transfer, space charge traps, and filament conduction. In addition, recent studies of conjugated polymers for memory device applications are also reviewed, discussed, and differentiated based on the mechanisms and structural design. Moreover, the electrical conditions of conjugated polymers can be further fine-tuned by careful design and synthesis based on the switching mechanisms. The review also emphasizes and demonstrates the structure-memory properties relationship of donor-acceptor conjugated polymers for advanced memory device applications. [ABSTRACT FROM AUTHOR]

We report solid iodine as a precursor additive for achieving purified organometallic perovskite crystals. By adding iodine, we found that the reaction can be pushed toward pure iodine phase rather than the kinetically favored chlorine phase. This approach can be applied in large crystalline perovskite solar cells and improved the average efficiency from 9.83% to 15.58%. [ABSTRACT FROM AUTHOR]

We report solid iodine as a precursor additive for achieving purified organometallic perovskite crystals. By adding iodine, we found that the reaction can be pushed toward pure iodine phase rather than the kinetically favored chlorine phase. This approach can be applied in large crystalline perovskite solar cells and improved the average efficiency from 9.83% to 15.58%. [ABSTRACT FROM AUTHOR]

State-of-the-art photovoltaics use high-purity, large-area, wafer-scale single-crystalline semiconductors grown by sophisticated, high-temperature crystal growth processes. We demonstrate a solution-based hot-casting technique to grow continuous, pinhole-free thin films of organometallic perovskites with millimeter-scale crystalline grains. We fabricated planar solar cells with efficiencies approaching 18%, with little cell-to-cell variability. The devices show hysteresis-free photovoltaic response, which had been a fundamental bottleneck for the stable operation of perovskite devices. Characterization and modeling attribute the improved performance to reduced bulk defects and improved charge carrier mobility in large-grain devices. We anticipate that this technique will lead the field toward synthesis of wafer-scale crystalline perovskites, necessary for the fabrication of high-efficiency solar cells, and will be applicable to several other material systems plagued by polydispersity, defects, and grain boundary recombination in solution-processed thin films. [ABSTRACT FROM AUTHOR]

Noble metal nanoparticles (MNPs) have attracted continuous attention due to their promising applications in chemistry, physics, bioscience, medicine and materials science. As an alternative to conventional solution chemistry routes, MNPs can be directly synthesized through a conjugated polymer (CP) mediated technique utilizing the redox chemistry of CPs to chemically reduce the metal ions and modulate the size, morphology, and structure of the MNPs. The as-prepared multifunctional CP-MNP nanocomposites have shown application potentials as highly sensitive surface enhanced Raman spectroscopy (SERS) substrates, effective heterogeneous catalysts for organic synthesis and electrochemistry, and key components for electronic and sensing devices. In this tutorial review, we begin with a brief introduction to the chemical nature and redox properties of CPs that enable the spontaneous reduction of noble metal ions to form MNPs. We then focus on recent progress in control over the size, morphology and structure of MNPs during the conjugated polymer mediated syntheses of CP-MNP nanocomposites. Finally, we highlight the multifunctional CP-MNP nanocomposites toward their applications in sensing, catalysis, and electronic devices. [ABSTRACT FROM AUTHOR]

Surface plasmon assisted catalysis (SPAC) reactions of 4-aminothiophenol (4ATP) to and back from 4,4'-dimercaptoazobenzene (DMAB) have been investigated by single particle surface enhanced Raman spectroscopy, using a self-designed gas flow cell to control the reductive/oxidative environment over the reactions. Conversion of 4ATP into DMAB is induced by energy transfer (plasmonic heating) from surface plasmon resonance to 4ATP, where O2 (as an electron acceptor) is essential and H2O (as a base) can accelerate the reaction. In contrast, hot electron (from surface plasmon decay) induction drives the reverse reaction of DMAB to 4ATP, where H2O (or H2) acts as the hydrogen source. More interestingly, the cyclic redox between 4ATP and DMAB by SPAC approach has been demonstrated. This SPAC methodology presents a unique platform for studying chemical reactions that are not possible under standard synthetic conditions. [ABSTRACT FROM AUTHOR]

Surface plasmon assisted catalysis (SPAC) reactions of 4-aminothiophenol (4ATP) to and back from 4,49-dimercaptoazobenzene (DMAB) have been investigated by single particle surface enhanced Raman spectroscopy, using a self-designed gas flow cell to control the reductive/oxidative environment over the reactions. Conversion of 4ATP into DMAB is induced by energy transfer (plasmonic heating) from surface plasmon resonance to 4ATP, where O2 (as an electron acceptor) is essential and H2O (as a base) can accelerate the reaction. In contrast, hot electron (from surface plasmon decay) induction drives the reverse reaction of DMAB to 4ATP, where H2O (or H2) acts as the hydrogen source. More interestingly, the cyclic redox between 4ATP and DMAB by SPAC approach has been demonstrated. This SPAC methodology presents a unique platform for studying chemical reactions that are not possible under standard synthetic conditions. [ABSTRACT FROM AUTHOR]

We demonstrate that photon antibunching observed for individual nanocrystal quantum dots (NQDs) can be transformed into photon bunching characterized by super-Poissonian statistics when they are coupled to metal nanostructures (MNs). This observation indicates that, while the quantum yield of a biexciton (Q2x) is lower than that of a single exciton (Q1X) in freestanding NQDs, Q2X becomes greater than Q1X in NQDs coupled to MNs. This unique phenomenon is attributed to metal-induced quenching with a rate that scales more slowly with exciton multiplicity than the radiative decay rate and dominates over other nonradiative decay channels for both single excitons and biexcitons. [ABSTRACT FROM AUTHOR]

A simple one-pot reaction using in Situ chemically generated Na-naphthalenide as an electron reductant in the preferential generation of C602- is described. Trapping of C602- intermediate with 2 molar equiv of sterically hindered 2-bronio-2-methylmalonate ester afforded two singly bonded fullerenyl hisadducts Cse[-CMe(CO2Et)2]2 in 35% and 7% yield, respectively. The regiochemistry of these two products was determined to be 1,4and 1,16-bisadducts, respectively, by NMR, UV-vis-NIR, LCMS, and X-ray single crystal structural analysis. The minor 1,16-bisadduct 2 exhibits long wavelength absorption bands in the near-jR region and prominent electron-accepting characteristics as compared with those of the major 1,4-bisadduct and pristine Cse. As revealed by DFT calculation, we propose that the origin of these unusual characters of 2 arises from the moiety of [18π ]-trannulene, in close resemblance to that of the highly symmetrical emerald green 1,1 6,29,38,43,60-hexaadduct of Cse, EF-6MC,,. Accordingly, we anticipate a fast progressive formation of plausible 1,16-bisadduct-like intermediate moieties on a Cse cage as the precursor structure leading to the formation of EF-6MC,,, by taking the corresponding regiochemistry and electronic properties into account. [ABSTRACT FROM AUTHOR]

We report a facile synthesis of large-area homogeneous three-dimensional (3D) Ag nanostructures on Au-supported polyaniline (PANI) membranes through a direct chemical reduction of metal ions by PANI. The citric acid absorbed on the Au nuclei that are prefabricated on PANI membranes directs Ag nanoaprticles (AgNPs) to self-assemble into 3D Ag nanosheet structures. The fabricated hybrid metal nanostructures display uniform surface-enhanced Raman scattering (SERS) responses throughout the whole surface area, with an average enhancement factor of 106−107. The nanocavities formed by the stereotypical stacking of these Ag nanosheets and the junctions and gaps between two neighboring AgNPs are believed to be responsible for the strong SERS response upon plasmon absorption. These homogeneous metal nanostructure decorated PANI membranes can be used as highly efficient SERS substrates for sensitive detection of chemical and biological analytes. [ABSTRACT FROM AUTHOR]

We report reversible thermochromism of a conjugated polymer, poly{2,5-bis[3-(N,N-diethylamino)-1-oxapropyl]-1,4-phenylenevinylene} (DAO-PPV), in diluted solutions of toluene and 1,2-dichlorobenzene. By means of temperature- and solvent-dependent steady-state spectroscopy, picosecond time-resolved photoluminescence spectroscopy, and dynamic light scattering, we provide new insights into the role of polymer aggregates in defining the thermochromic behavior of PPVs. We find DAO-PPV to exhibit a low temperature state with vibronically structured red visible absorption and emission spectra. Structurally, this low temperature state is a densely packed and disordered polymer aggregate, which contains a fraction of well-ordered, packed polymer chains. These ordered regions serve as low energy trap sites for the more disordered regions in the aggregate, thus regulating the final emission of the aggregate and imposing a vibronically resolved emission spectrum, which is usually associated with emission from one or a few chromophores. The high temperature state of DAO-PPV is a loose aggregate, with structureless absorption and emission spectra in the green visible range. Structurally, the loose aggregate is a well-solvated aggregate retaining the physical dimension of the dense aggregate but for which interchain interactions are diminished with the increase of temperature. As a result, the spectroscopic behavior of the loose aggregate is very similar if not identical to that of the single polymer chain. Increased solubility untangles polymer aggregates into single, dispersed, polymer chains, as we demonstrate here for DAO-PPV in 1,2-dichlorobenzene and at high temperature. [ABSTRACT FROM AUTHOR]

Colloidal nanocrystal quantum dots (NQDs) of narrow band gap materials are of substantial general interest because of their unparalleled potential as infrared fluorophores. While PbSe NQDs are a promising class of infrared-active nanocrystals due to high emission quantum yields and a wide useful spectral range, typical synthetic methods are sensitive to a variety of factors, including the influence of solvent/ligand impurities that render reproducibility difficult. In this work, we specifically examine the effects of diphenylphosphine and 1,2-hexadecanediol, as surrogates for putative trioctylphosphine-based reducing impurities, on the synthesis of PbSe NQDs. Specifically, we compare their influence on NQD size, chemical yield, and photoluminescence quantum yield. While both additives substantially increase the chemical yield of the synthesis, they demonstrate markedly different effects on emission quantum yield of the product NQDs. We further examine the effects of reaction temperature and oleic acid concentration on the diol-assisted synthesis. Increased oleic acid concentration led to somewhat higher growth rates and larger NQDs but at the expense of lower chemical yield. Temperature was found to have an even greater effect on growth rate and NQD size. Neither temperature nor oleic acid concentration was found to have noticeable effects on NQD emission quantum yield. Finally, we use numerical simulations to support the conjecture that the increased yield is likely a result of faster monomer formation, consistent with the activation of an additional reaction pathway by the reducing species. [ABSTRACT FROM AUTHOR]

In this work we build on prior studies of the novel water-soluble cationic conjugated polymer known as “P2” (poly{2,5-bis[3-( N, N, N-triethylammonium bromide)-1-oxapropyl]-1,4-phenylenevinylene}) with a focus on its incorporation into thin films for such applications as photovoltaics or electroluminescent devices. Multilayer assemblies were constructed using P2, the anionic surfactant sodium dodecyl sulfate (SDS), and the polyanion poly(sodium 4-styrene-sulfonate) (PSS) using the technique of layer-by-layer electrostatic self-assembly (LBL-ESA). SDS was observed to affect the layer thicknesses and absorbance characteristics of the films. We show that the optical properties and photo-oxidative resistance can be improved by varying the SDS content in the assemblies. Specifically, the surfactant-complexed poly( p-phenylenevinylene) (PPV) shows an enhanced absorption at longer wavelengths as well as improved photostability. Therefore, our work may have broad implications on the development of stable PPV-based materials in general and their efficient integration into thin films technologies. [ABSTRACT FROM AUTHOR]

We report a facile method toward preparation of conducting polymer-supported Pd nanoparticles by in situ reducing the palladium salt [Pd(NO 3) 2] on the surface of polyaniline (PANI) film/membrane. The palladium(0) particles distribute evenly on the PANI surfaces. The size and morphology of Pd particles are dependent on the nature of the substrate surfaces. The palladium (Pd) particles on the PANI membrane surfaces have a rough surface morphology with a size distribution of ∼200 nm, and the Pd particles on the PANI film have a smooth surface with a size distribution of ∼500 nm. These Pd particles are in fact conglomerates of much smaller nanoparticles with an average size distribution of 13 nm. Pd nanoparticles exhibit efficient catalytic activity toward hydrogenation of alkynes and cinnamaldehyde with high selectivities dominated by a kinetic mechanism. Moreover, our results suggest that the variation in particle morphology resulting from substrates leads to differences in their catalytic efficiency presumably due to the difference in surface area. The PANI-supported Pd nanoparticles are robust and can be reused at least seven times without the significant loss of its catalytic activity and selectivity. [ABSTRACT FROM AUTHOR]

In this work, we investigate the emission and absorbance properties of the novel water-soluble cationic conjugated polymer poly2,5-bis3-(N,N,N-triethylammonium bromide)-1-oxapropyl-1,4-phenylenevinylene, denoted here as P2, in the presence of varying amounts of the anionic surfactant sodium dodecylsulfate (SDS). We show that the absolute photoluminescence quantum efficiency (PLQE), the absorption wavelength, and the emission wavelength of an aqueous solution of P2 can be adjusted according to the surfactant/polymer ratio in aqueous solution. In particular, we show that the addition of SDS to P2 increases the polyelectrolyte's PLQE to ∼40%. An observed red shift in the emission spectra upon addition of the surfactant is attributed to the reduction in electrostatic repulsive interactions between side chains that minimize the benzene ring twisting along the backbone structure. At the surfactant's critical micelle concentration, the P2 chains wrap around the outer surface of the SDS micelles. This work has implications on the development of new stable poly(p-phenylenevinylene)-based photovoltaic and electroluminescent materials with tunable optical properties. [ABSTRACT FROM AUTHOR]

Biosensing applications of single-walled carbon nanotubes have been demonstrated in solid-state device structures. Bioanalyte sensing schemes based on coupling of reversible nanotube fluorescence quenching to redox reactions paired to enzymatic peroxide generation have also been pursued. Here we show a new approach to highly sensitive nanotube-based optical sensing. Single-walled carbon nanotubes interacting with dye–ligand conjugates—a redox-active dye molecule that is covalently bound to a biological receptor ligand (such as biotin in this case)—showed fluorescence quenching. Further interaction between the receptor ligand on the conjugates and target analytes (avidin in this case) induced the recovery of the quenched fluorescence, forming the basis of the sensing scheme. Nanomolar sensitivity was attained with high specificity for the target analyte. This is a versatile approach because a wide range of conjugation possibilities exists between the potential receptors and redox quenchers. [ABSTRACT FROM AUTHOR]

We report here the synthesis and characterization of two new conjugated polymers:  poly2,5-bis3-(N,N-diethylammonium acetate)-1-oxapropyl-1,4-phenylenevinylene (P1‘) and poly2,5-bis3-(N,N,N-triethylammonium bromide)-1-oxapropyl-1,4-phenylenevinylene (P2). Both polymers exhibit unique pH-dependent optical properties in aqueous solution. These pH-dependent optical properties are attributed to the mutual electrostatic repulsions of positive charges pendent on the benzene rings. This electrostatic repulsion leads to an increased or decreased torsional angle in the conjugated backbone, thus affecting the effective conjugation length of these polymers. The UV−vis spectra of P1in various pH solutions exhibit a near-isosbestic point, which indicates changes in the composition of the two distinct conformations (the charged and the neutral forms). The transition between the highly charged state and the neutral state was clearly observed in the UV−vis and photoluminescence studies on both P1and P2. This transition is particularly sensitive in the pH range from 6.2 to 7.0, a range that would allow the detection of minor environmental changes. P2has a quantum efficiency of 14% in water, which is considered to be relatively high among water-soluble PPVs. [ABSTRACT FROM AUTHOR]

Conducting poly-(phenylene vinylene) honeycomb hexagonal framework of large area (1 mm2) are demonstrated by the breath-figure technique. These honeycomb frameworks are then dopped with fullerenes to undergo dramatic quenching by charge transfer. [ABSTRACT FROM AUTHOR]