Selective syntheses of vinylenedithiathiophenes (VDTTs) and dithieno[2,3-b;2′,3′-d]thiophenes (DTTs); building blocks for π-conjugated systems

Selective syntheses of 3,4-vinylenedithiathiophenes (VDTTs) and dithieno[2,3-b;2′,3′-d]thiophenes (DTTs), having Ph, 4-CH₃OC₆H₄, 4-BrC₆H₄, 4-NO₂C₆H₄ and 4-(CH₃)₂NC₆H₄ groups, were achieved through the reaction of 1,8-diketone with phosphorus decasulfide (P₄S₁₀). The reaction could be shifted between VDTT and DTT by adding base (sodium bicarbonate) or acid (para-toluenesulfonic acid), respectively, to the reaction mixture. While the VDTTs were obtained in moderate yields, an important achievement has been made with the syntheses of the DTTs, obtaining them in higher yields compared with the previous report. Polymers of the VDTTs, which are the analogues of ethylenedioxythiophene, EDOT, were prepared using FeCl₃. Unfortunately, all attempts for their electropolymerization failed. Spin density calculations revealed that none of the VDTTs had a significant positive spin density at the ‘α’ carbon atoms of the thiophene ring. Considering their solubility and functional groups, which could be further derivatized, they are useful building blocks for the preparation of new organic materials.     

High resolution electronic absorption spectra of anisole and phenoxyl radical

High resolution absorption spectra of anisole and phenoxyl radical has been recorded in the vapor phase at room temperature by flash photolysis technique, and subsequent reactions have been investigated by kinetic spectroscopy. It was possible to follow the kinetics of the radical's decay which occurred predominantly by bimolecular recombination. The concentration of the phenoxyl radical calculated from the concentration of diphenoxyl molecules formed in the reaction cell during the optical pumping. The absolute extinction coefficient of this radical was measured from the absorption band at 291 nm, and found to be 0.95 x 10(+4) mol(-1) 1 cm(-1).     

Release Profiles of Tricalcium Phosphate Nanoparticles from Poly(L‐lactic acid) Electrospun Scaffolds with Single Component,Core–Sheath,or Porous Fiber Morphologies: Effects on hASC Viability and Osteogenic Differentiation

Functional PLA scaffolds are created with single component, core–sheath, or porous fiber morphology and doped with TCP nanoparticles to study the release profiles for use in bone tissue engineering applications. Pharmacokinetic analyses are performed for the three different nanofibrous structures after doping with TCP. Results indicate that single component and porous fiber scaffolds exhibit an initial‐burst release profile whereas core–sheath fibers show a steady release. All scaffolds are then seeded with human adipose‐derived stem cells (hASC), which remain viable and continue proliferation on all nanofibrous morphologies for up to 21 d. Osteogenic differentiation of hASC and cell‐mediated calcium accretion are largest on porous fibers.

     

Water‐Assisted Vapor Deposition of PEDOT Thin Film

The synthesis and characterization of poly(3,4‐ethylenedioxythiophene) (PEDOT) using water‐assisted vapor phase polymerization (VPP) and oxidative chemical vapor deposition (oCVD) are reported. For the VPP PEDOT, the oxidant, FeCl₃, is sublimated onto the substrate from a heated crucible in the reactor chamber and subsequently exposed to 3,4‐ethylenedioxythiophene (EDOT) monomer and water vapor in the same reactor. The oCVD PEDOT was produced by introducing the oxidant, EDOT monomer, and water vapor simultaneously to the reactor. The enhancement of doping and crystallinity is observed in the water‐assisted oCVD thin films. The high doping level observed at UV–vis–NIR spectra for the oCVD PEDOT, suggests that water acts as a solubilizing agent for oxidant and its byproducts. Although the VPP produced PEDOT thin films are fully amorphous, their conductivities are comparable with that of the oCVD produced ones.

     

Butane‐1‐sulfonic acid immobilized on magnetic Fe3O4@SiO2 nanoparticles: A novel and heterogeneous catalyst for the one‐pot synthesis of barbituric acid and pyrano[2,3‐d] pyrimidine derivatives in aqueous media

Butane‐1‐sulfonic acid immobilized on magnetic Fe₃O₄@SiO₂ nanoparticles (Fe₃O₄@SiO₂‐Sultone) was easily prepared via direct ring opening of 1,4‐butanesultone with nanomagnetic Fe₃O₄@SiO₂. The prepared reagent was characterized and used for the efficient promotion of the synthesis of barbituric acid and pyrano[2,3‐d] pyrimidine derivatives. All reactions were performed under mild and completely heterogeneous reaction conditions affording products in good to high yields. The catalyst is easily isolated from the reaction mixture by magnetic decantation and can be reused at least eight times without significant loss in activity.     

Synthesis of bistriphenylamine‐ and benzodithiophene‐based random conjugated polymers for organic photovoltaic applications

In this study, donor–acceptor random polymers containing benzotriazole acceptor and bistriphenylamine and benzodithiophene donors, P1 and P2 , were successfully synthesized by Stille coupling polymerization. The effect of bistriphenylamine moiety and thiophene π‐conjugated linker on electrochemical, spectroelectrochemical, and optical behaviors of the polymers were investigated. Optoelectronic properties and photovoltaic performance of the polymers were examined under the illumination of AM 1.5G, 100 mW cm^?2. The polymers were characterized by cyclic voltammetry, UV‐Vis‐NIR absorption spectroscopy, gel permeation chromatography. HOMO/LUMO energy levels of P1 and P2 were calculated as ?5.47 eV/–3.41 eV and ?5.43 eV/–3.27 eV, respectively. Bulk heterojunction type solar cells were constructed using blends of the polymers (donor) and [6,6]‐phenyl C₇₁ butyric acid methyl ester (PC₇₁BM) (acceptor). Photovoltaic studies showed that the highest power conversion efficiency of these photovoltaic devices were recorded as 3.50% with open circuit voltage; 0.79 V, short circuit current; 9.45 mA cm^?2, fill factor; 0.53 for P1 :PC₇₁BM (1:2, w/w) in 3% o‐dichlorobenzene (o‐DCB) solution and 3.15% with open circuit voltage; 0.75 V, short circuit current; 8.59 mA cm^?2, fill factor; 0.49 for P2 :PC₇₁BM (1:2, w/w) in 2% chlorobenzene (CB) solution. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 3705–3715     

Determination of lead in hair and its segmental analysis by solid sampling electrothermal atomic absorption spectrometry

A rapid and practical solid sampling electrothermal atomic absorption spectrometric method was described for the determination of lead in scalp hair. Hair samples were washed once with acetone; thrice with distilled-deionized water and again once with acetone and dried at 75 °C. Typically 0.05 to 1.0 mg of dried samples were inserted on the platforms of solid sampling autosampler. The effects of pyrolysis temperature, atomization temperature, the amount of sample as well as addition of a modifier (Pd/Mg) and/or auxiliary digesting agents (hydrogen peroxide and nitric acid) and/or a surfactant (Triton X-100) on the recovery of lead were investigated. Hair samples were washed once with acetone; thrice with distilled-deionized water and again once with acetone and dried at 75 °C. Typically 0.05 to 1.0 mg of dried samples were inserted on the platforms of solid sampling autosampler. The limit of detection for lead (3σ, N = 10) was 0.3 ng/g The addition of modifier, acids, oxidant and surfactant hardly improved the results. Due to the risk of contamination and relatively high blank values, the lead in hair were determined directly without adding any reagent(s). Finally, the method was applied for the segmental determination of lead concentrations in hair of different persons which is important to know when and how much a person was exposed to the analyte. For this purpose, 0.5 cm of pieces were cut along the one or a few close strands and analyzed by solid sampling.     

On Hölder continuous Riemannian and Finsler metrics

We discuss smoothness of geodesics in Riemannian and Finsler metrics.

     

Wavelength and coherence effects on the growth mechanism of silicon nanopillars and their use in the modification of spontaneous lifetime emission of BODIPY dye molecules

Silicon nanopillars are grown by an electrochemical anodization of p-type silicon wafers at low current densities in a hydrofluoric acid solution. CW, white light, and various UV pulsed lasers are employed as illumination sources in sample preparation to study wavelength and coherence effects on the growth mechanism of the nanopillars. Coherence is observed to be the foundation of regularity in obtaining conical shapes. The pillar size is found to be almost linearly proportional to the employed illumination wavelength during their growth. BODIPY dye molecules are chemically attached to these silicon nanopillars and the radiative decay rates are investigated by means of a time-resolved fluorescence experiment. The decay rate of the dye molecules embedded in the vicinity of various size pillar tips is significantly affected due to different apex angles of the conical nature. It is demonstrated that the pillar size and the separation between pillars can be adjusted if one uses a coherent light source with an appropriate wavelength during the course of fabrication process. Since change in the decay rate is due to tips of the pillars only, separation of a few micrometers between pillar tips allows one to directly monitor a dye, which is embedded to the tip of a single nanopillar, via a confocal microscopic method for the spontaneous lifetime measurements, without having needed to any extra efforts for an in situ imaging process. It is observed that as the pillar size gets smaller, the inhibition in the spontaneous lifetime of BODIPY is more pronounced. In addition, a more regular pillar structure yields nonvarying decay rates of the dye molecules throughout the silicon sample.