Luminescent supramolecular polymers: Cd2+-directed polymerization and properties

A family of supramolecular polymers was prepared via Cd2+-directed self-assembly polymerization of his (2,2':6',2 ''-terpyridine)-based ligand monomers, using oligofluorenes and triphenylamine as bridges under mild conditions. The polymers were fully characterized using thermogravimetric analysis, inherent viscosity, electrochemical measurements, UV-visible spectroscopy, photoluminescence (PL) and electroluminescence (EL). Polymers with oligofluorenes as spacers exhibited blue emission (434-442 nm) in dimethyl acetamide (DMAc) solution, while polymers with triphenylamine as spacer presented an emission peak at 494 nn in DMAc solution. Complexation polymerization of bis(2,2':6',2 ''-terpyridine)-based ligand monomers with cadmium(II) improved fluorescence quantum yields dramatically, and the film PL quantum yields of these polymers were about 0.38-0.54. Single-layer light-emitting diodes were fabricated with the configuration indium tin oxide (ITO)/polymer/Ca/Al; the EL showed green emission and the onset voltages of the devices were 8-11 V.

Electrocatalytic reduction of 1,2-diiodoethane by anions of supramolecular complex of (beta-CD)(2)/C-60 in DMF solution

The homogeneous electrocatalytic reduction of 1,2-diiodoethane by anions of the supramolecular complex of (beta-CD)(2)/C-60 in DMF solution is reported. The results show that the trianion of (beta-CD)(2)/C-60 exhibits electrocatalytic behavior towards the reduction of 1,2-diiodoethane, whereas the diani on is unable to reduce the diiodoethane. The second-order catalytic rate constant in DMF solution was determined to be 3.1 x 10(5) M-1 s(-1) by analysis of voltammetric responses under pseudo-first-order conditions with respect to (beta-CD)(2)/C-60. The results suggest that the host beta-cyclodextrin molecules have little effect on the electrocatalytic ability of the encapsulated C-60 toward organic halides.

Controllable synthesis of highly luminescent and monodisperse CdS nanocrystals by a two-phase approach under mild conditions

Highly luminescent and monodisperse CdS nanocrystals (see Figure) have been synthesized using a two-phase approach. The synthesis of CdS nanocrystals at the liquid-liquid interface was easy, safe, and highly reproducible, and the reaction conditions were mild and controllable.

Temperature and pressure dependence of phase separation of trans-decahydronaphthalene/polystyrene solution

The cloud-point temperatures (T-c1's) of ti-ans-decahydronaphthalene (TD)/polystyrene (PS, M-w = 270 kg/mol) solutions were determined by fight scattering measurements over a range of temperatures (1-16 degreesC), pressures (100-900 bar), and compositions (4.2-21.6 vol% polymer). The system phase separates upon cooling and the T-c1 was found to increase with the rising pressure for the constant composition. In the absence of special effects this finding indicates positive excess volumes. The special attention was paid to the demixing temperatures as a function of the pressure for the different polymer solutions and the plots in the T-volume fraction plane and P-volume fraction plane. The cloud-point curves of polymer solutions under changing pressures were observed for different compositions, demonstrates that the TD/PS system exhibits UCST (phase separation upon cooling) behavior. With this data the phase diagrams under pressure were calculated applying the Sanchez-Lacombe (SL) lattice fluid theory. Furthermore, the cause of phase separation, i.e., the influence of Flory-Huggins (FH) interaction parameter under pressure was investigated.

Conducting probe atomic force microscopy investigation of anisotropic charge transport in solution cast PBD single crystals induced by an external field

2-(4-Biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxdiazole (PBD) is a good electron-transporting material and can form single crystals from solution. In this work, solution cast PBD single crystals with different crystallographic axes (b, c) perpendicular to the Au/S substrates in large area are achieved by controlling the rate of solvent evaporation in the presence and absence of external electrostatic field, respectively. The orientation of these single crystals on Au/S substrate was characterized by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Conducting probe atomic force microscopy (CP-AFM) was used to measure the charge transport characteristics of PBD single crystals grown on Au/S substrates. Transport was measured perpendicular to the substrate between the CP-AFM tip and the Au/S substrate. The electron mobility of 3 x 10(-3) cm(2)/(V s) for PBD single crystal along crystallographic b-axis is determined. And the electron mobility of PBD single crystal along the c-axis is about 2 orders of magnitude higher than that along the b-axis due to the anisotropic charge transport at the low voltage region.

Extraction mechanism of La3+ from hydrochloric acid solution using Cyanex 302

The solvent extraction of La3+ from hydrochloric acid solutions was investigated using his (2, 4, 4-trimethylpentyl) monothiophosphinic acid (Cyanex 302, HL) as an extractant. The effect of equilibrium of aqueous acidity on extraction of La3+ using Cyanex 302 In different diluents was discussed. The effects of extractant concentration and chloride ion on the extraction reaction were also studied. Stoichiometry of the extraction reactions and the nature of metal complexes formed were determined using slope analysis technique and IR measurement.

Formation equilibria of ternary metal complexes with citric acid and glutamine (alanine) in aqueous solution

The species and their formation constants in the ternary, systems were obtained by the Scogs2 software from potentiometric titration data. The Comics software was used to calculate the distribution of species in the ternary systems. MLXH, MLXH2 and MLXH3 are the common species in these systems. The coordination behaviors of the rare earths are very similar and their stability is closely matched. The ternary rare earth complexes are more stable than the corresponding ternary complexes of calcium. The ternary zinc complex with glutamine as the secondary ligand is more stable than the corresponding complexes of rare earths, but the ternary complex with alanine as the secondary ligand shows an inverse trend. The distributions of species in the ternary systems vary with pH changing. A prediction can be made that exogenous rare earths can affect the species of Ca and Zn in human body.

Carbon nanotubes selective destabilization of duplex and triplex DNA and inducing B-A transition in solution

Single-walled carbon nanotubes (SWNTs) have been considered as the leading candidate for nano-device applications ranging from gene therapy and novel drug delivery to membrane separations. The miniaturization of DNA-nanotube devices for biological applications requires fully understanding DNA-nanotube interaction mechanism. We report here, for the first time, that DNA destabilization and conformational transition induced by SWNTs are sequence-dependent. Contrasting changes for SWNTs binding to poly[dGdC]:poly[dGdC] and poly[dAdT]:poly[dAdT] were observed. For GC homopolymer, DNA melting temperature was decreased 40 degrees C by SWNTs but no change for AT-DNA. SWNTs can induce B-A transition for GC-DNA but AT-DNA resisted the transition. Our circular dichroism, competitive binding assay and triplex destabilization studies provide direct evidence that SWNTs induce DNA B-A transition in solution and they bind to the DNA major groove with GC preference.

Effects of chain flexibility on polymer conformation in dilute solution studied by lattice Monte Carlo simulation

Effects of chain flexibility on the conformation of homopolymers in good solvents have been investigated by Monte Carlo simulation. Bond angle constraint coupled with persistence length of polymer chains has been introduced in the modified eight-site bond fluctuation simulation model. The study about the effects of chain flexibility on polymer sizes reveals that the orientation of polymer chains under confinement is driven by the loss of conformation entropy. The conformation of polymer chains undergoing a gradual change from spherical iso-diametric ellipsoid to rodlike iso-diametric ellipsoid with the decrease of polymer chain flexibility in a wide region has been clearly illustrated from several aspects. Furthermore, a comparison of the freely jointed chain (FJC) model and the wormlike chain (WLC) model has also been made to describe the polymer sizes in terms of chain flexibility and quasi-quantitative boundary toward the suitability of the models.

Surface-enhanced Raman scattering studies on aggregated silver nanoplates in aqueous solution

Four different sizes of citrate-protected silver nanoplates with the corresponding in-plane dipole resonance band at 530, 619, 778, and 858 nm, respectively, are synthesized for surface-enhanced Raman scattering (SERS) study. Their aggregation behaviors are monitored by use of UV-vis spectroscopy. During the aggregation process, a marked red shift of the in-plane dipole resonance of silver nanoplates is observed, whereas other resonance modes of them only have small alterations in the site or intensity. Aggregated silver nanoplates can serve as active SERS substrates with an enhancement factor of about 4.5 x 10(5) using 2-aminothiophenol as a probing molecule. The SERS performance of silver nanoplates is even superior to the commonly used Lee-Meisel silver colloid, making them very attractive for SERS applications.

Inverted to normal phase transition in solution-cast polystyrene-poly(methyl methacrylate) block copolymer thin films

We have investigated the inverted phase formation and the transition from inverted to normal phase for a cylinder-forming polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer in solution-cast films with thickness about 300 nm during the process of the solution concentrating by slow solvent evaporation. The cast solvent is 1, 1,2,2-tetrachloroethane (Tetra-CE), a good solvent for both blocks but having preferential affinity for the minority PMMA block. During such solution concentrating process, the phase behavior was examined by freeze-drying the samples at different evaporation time, corresponding to at different block copolymer concentrations, phi. As phi increases from similar to 0.1 % (nu/nu), the phase structure evolved from the disordered sphere phase (DS), consisting of random arranged spheres with the majority PS block as I core and the minority PMMA block as a corona, to ordered inverted phases including inverted spheres (IS), inverted cylinders (IC), and inverted hexagonally perforated lamellae (IHPL) with the minority PMMA block comprising the continuum phase, and then to the lamellar (LAM) phase with alternate layers of the two blocks, and finally to the normal cylinder (NC) phase with the majority PS block comprising the continuum phase. The solvent nature and the copolymer solution concentration are shown to be mainly responsible for the inverted phase formation and the phase transition process.

Crystallization and phase behavior of crystalline syndiotactic 1,2-polybutadiene/isotactic polypropylene blends in solution-cast thin films

Crystallization and phase behavior in solution-cast thin films of crystalline syndiotactic 1,2-polybutadiene (s-1,2-PB) and isotactic polypropylene (i-PP) blends have been investigated by transmission electron microscopy (TEM), atomic force microscopy (AFM) and field-emission scanning electron microscopy (FESEM) techniques. Thin films of pure s-1,2-PB consist of parallel lamellae with the c-axis perpendicular to the film plane and the lateral scale in micrometer size, while those of i-PP are composed of cross-hatched and single-crystal-like lamellae. For the blends, TEM and AFM observations show that with addition of i-PP, the s-1,2-PB long lamellae become bended and i-PP itself tends to form dispersed convex regions oil a continuous s-1,2-PB phase even when i-PP is the predominant component, which indicates a strong phase separation between the two polymers during film formation. FESEM micrographs of both lower and upper surfaces of the films reveal that the s-1,2-PB lamellae pass through i-PPconvex regions from the bottom, i.e. the dispersed i-PP regions lie on the continuous s-1,2-PB phase. The structural development is attributed to an interplay of crystallization and phase separation of the blends in the film forming process.

Rapid solution and solid phase synthesis of monodisperse oligo[(1,4-phenyleneethynylene)-alt-(2,5-thiopheneethynylene)]s

Monodisperse oligo[(1,4-phenyleneethynylene)-alt-(2,5-thiopheneethynylene)]s, new candidates for molecular wires, were rapidly synthesized via an iterative divergent/convergent doubling strategy in solution as well as on Merrifield's resin.