Synthesis and characterization of a new phenanthrenequinoxaline‐based polymer for organic solar cells

Two donor–acceptor (D‐A) conjugated polymers, PQx and PphQx, composed of alkylthienyl‐substituted benzo[1,2‐b:4,5‐b']dithiophene (BDTT) as the electron donor and the new electron acceptors quinoxaline (Qx) or phenanthrenequinoxaline (phQx), were synthesized with Stille cross‐coupling reactions. The number‐averaged molecular weights (M_n) of PQx and PphQx were found to be 25.1 and 23.2 kDa, respectively, with a dispersity of 2.6. The band‐gap energies of PQx and PphQx are 1.82 and 1.75 eV, respectively. These results indicate that, because phQx units have highly planar structures, their inclusion in D‐A polymers will be a very effective method for increasing the polymers' effective conjugation lengths. The hole mobilities of PQx and PphQx were determined to be 5.0 × 10^?5 and 2.2 × 10^?4 cm² V^?1 s^?1, respectively. A polymer solar cell device prepared with PphQx as the active layer was found to exhibit a power conversion efficiency (PCE) of 5.03%; thus, the introduction of phQx units enhanced both the short circuit current density and PCE of the device. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2804–2810     

Oxidative Dissolution of Silver Nanoparticles by Biologically Relevant Oxidants: A Kinetic and Mechanistic Study

The oxidative dissolution of silver nanoparticles (AgNPs) plays an important role in the synthesis of well‐defined nanostructured materials, and may be responsible for their activities in biological systems. In this study, we use stopped‐flow spectrophotometry to investigate the kinetics and mechanism of the oxidative dissolution of AgNPs by H₂O₂ in quasi‐physiological conditions. Our results show that the reaction is first order with respect to both [Ag⁰] and [H₂O₂], and parallel pathways that involve the oxidation of H₂O₂ and HO₂^? are proposed. The order of the reaction is independent of the size of the AgNPs (≈5–20 nm). The rate of dissolution increases with increasing pH from 6.0 to 8.5. At 298 K and I=0.1 M , the value of k_b is five orders of magnitude higher than that of k_a (where k_a and k_b are the rate constants for the oxidative dissolution of AgNPs by H₂O₂ and HO₂^?, respectively). In addition, the effects of surface coating and the presence of halide ions on the dissolution rates are investigated. A possible mechanism for the oxidative dissolution of AgNPs by H₂O₂ is proposed. We further demonstrate that the toxicities of AgNPs in both bacteria and mammalian cells are enhanced in the presence of H₂O₂, thereby highlighting the biological relevance of investigating the oxidative dissolution of AgNPs.     

The effect of modification with fluorescent groups on the physicochemical characteristics of poly(alkylene oxides)

Covalent modification of poly(alkylene oxides), block copolymers of ethylene oxide and propylene oxide with M ∼ 2000, with fluororescein isothiocyanate or 7-nitrobenzo-2-oxadiazole taken in a ratio of 0.6–1.0 mol of label/mole of polymer leads to changes in the physical state of polymers and their solubility in water decreases, as well as the partition coefficient in the hexane-water system and the critical concentration of aggregation and dimensions of the formed particles.     

Synthesis and characterization of Eu<Superscript>3+</Superscript> doped Lu<Subscript>2</Subscript>O<Subscript>3</Subscript> nanophosphor using a solution-combustion method

Fine Eu³⁺-doped lutetium oxide (Lu₂O₃:Eu³⁺) nanophosphor were synthesized using a low-temperature solution-combustion method in a methyl-alcohol solution. The characteristics of the nanophosphors synthesized at various sintering temperatures with different Eu³⁺ concentrations were analyzed to determine the optimum synthesis conditions. Thermogravimetry/differential thermal analysis showed that Lu₂O₃:Eu³⁺ crystallizes completely when the dry powder is sintered at 500 °C. The Lu₂O₃:Eu³⁺ crystals had a cubic structure and monoclinic phase. The peak position of the luminescence spectrum did not differ with the concentration of Eu or the sintering temperature or atmosphere, whereas the luminescence intensity was strongly dependent on the concentration and sintering conditions.     

A Concise Total Synthesis of (+)‐Tetrabenazine and (+)‐α‐Dihydrotetrabenazine

Highly concise asymmetric total syntheses of (+)‐tetrabenazine ( 1 ), a drug for the treatment of chorea associated with Huntington’s disease, and of (+)‐α‐dihydrotetrabenazine ( 2 ), an active metabolite of 1 , have been accomplished. Our synthetic route features a trans‐selective enol etherification, followed by an unprecedented cation‐dependent aza‐Claisen rearrangement to establish the carbon framework and two stereogenic centers of tetrabenazine. The syntheses consist of seven steps (34 % overall yield) for (+)‐ 2 and eight steps (22 % overall yield) for (+)‐ 1 .     

Microfluidic preparation of dual stimuli-responsive microparticles and light-directed clustering

We present a simple fabrication of photo- and thermoresponsive microparticles with a narrow size distribution in the PDMS-based microfluidic device. The monodisperse water-in-oil (W/O) droplets of poly(N-isopropylacrylamide-co-spironaphthoxazine methacryloyl) (PNIPA-SPO) were formed at the T-junction channel of the device by adjusting the flow conditions of two immiscible solutions. Subsequently, the droplets were polymerized downstream of the channel under 365 nm UV irradiation in the presence of 2,2'-diethoxyacetophenone (DEAP, photoinitiator) and N,N'-methylenebisacrylamide (MBA, monomer and cross-linker). Being photosensitive, the polymerized microparticles progressively change their color when subjected to UV-vis irradiation. Above the LCST of the copolymer, the microparticles exhibited volume shrinkage accompanied by color deterioration. In addition, the UV light-driven clustering of the PNIPA-SPO copolymer was observed within the W/O droplet in the absence of photoinitiator, which contributed to variable microstructures from Janus to acorn-like and snowman-like morphologies. This work is the first attempt to unveil the photocontrolled asymmetric particle morphology by using the photoresponsive polymer.     

Nano‐ and Microstructure Fabrication by Using a Three‐Component System

Two‐component amphiphiles based on hydrogen‐bonded complexes between terephthaloylbisalanine (H₂TBA) and dodecylamine (DA) are able to self‐assemble into nano‐ and microsized superstructures in an aqueous solvent. It is possible to modulate the morphology of these self‐assembled superstructures by modifying the composition of the complexes, which can be achieved by changing the molar ratio of the two components or by changing the chirality of H₂TBA. For example, right‐handed microhelical ribbon structures were formed with L ‐TBA_1.0DA_2.0, whereas in the case of rac‐TBA_1.0DA_2.0, flat ribbonlike structures were observed. Although L ‐TBA_1.0DA_1.0 exhibited entangled fibrous structures, rac‐TBA_1.0DA_1.0 exhibited wire structures. Different ratios of H₂TBA and DA were self‐assembled into fiber‐, wire‐, and tubulelike superstructures, as well as monoclinic, columnar, and lamellar aggregation patterns. The self‐assembled superstructures of TBA_xDA_y were significantly changed by adding metal ions. Transition metal (Cd^II, Co^II, and Zn^II) complexes with L ‐TBA_xDA_y self‐assembled into rod‐, tubule‐, wire‐, and platelike superstructures. Metal‐ion complexes with rac‐TBA_xDA_y exhibited different superstructures. Our work suggests that it is possible to fabricate a wide variety of nano‐ and microsized superstructures by using two‐ and three‐component amphiphiles.     

The effect of Al2O3-coating coverage on the electrochemical properties in LiCoO2 thin films

The electrochemical properties of nanoscale Al₂O₃-coated LiCoO₂ thin films were examined as a function of the coating coverage. Al₂O₃-coated LiCoO₂ films showed enhanced cycle-life performance with increasing degree of coating coverage, which was attributed to the suppression of Co dissolution and F⁻ concentration in the electrolyte. Moreover, an Al₂O₃-coating layer with partial coverage clearly improved the electrochemical properties, even at 60 °C or with a water-contaminated electrolyte. Even though metal-oxide coating on LiCoO₂ has been actively investigated, the mechanisms of nanoscale coating have yet to be clearly identified. In this article, surface analysis suggested that the Al₂O₃-coating layer had transformed to an AlF₃ ∙3H₂O layer during cycling, which inhibited the generation of HF by scavenging H₂O molecules present in the electrolyte.     

Non-Invasive Measurements of Thickness of Superconductor Films by Using Two-Resonant-Mode Rutile Resonator

The film thickness should be known for extrazting the intrinsic surface resistance from the effective surface resistance as measured by using the dielectric resonator method. Thicknesses of 70 nm to 360 nm are measured for YBa2 Cu3 O7-δ films in a non-invasive way by using the two-resonant-mode dielectric resonator （TDR） method. A futile resonator with the respective resonant frequencies of 15.25-15.61 GHz and 15.10-15.37 GHz for the TE021 and the TE012 modes is used for this purpose. Differences between the values as measured by using the TDR technique and those measured by using a step profilometer appear to be less than 3%, which is smaller than the previous value of 5% as measured by using a 8. 6 GHz single-resonance mode futile resonator [Lee et al. J. Korean Phys. Soc. 54（2009）1619]. Merits of using the TDR method are discussed.     

Fabrication and Characterization of Multi-layer Heat Mirror with Photocatalytic Properties

A novel TiO2（5）/TiO2（buffer）/Ti（4）/Ag（3）/Ti（2）/TiO2（1） multi-layer film coating with corning glass is designed and fabricated by a dc magnetron sputtering method as a renovation of the well-known TiO2/Ti/Ag/Ti/TiO2 system in order to obtain a heat mirror system with photocatalytic properties due to sufficient thickness of the Ti02 layer. The outer TiO2 layer is fabricated in two steps, possibly claimed as two layers TiO2（5） and TiO2（buuer）, among which TiO2（buffer） the 70-nm-thick layer deposited in poor oxygen effectively minimizes the oxidation toward its neighbor Ti（4） layer. The optimal total thickness of the TiO2（5） and TiO（buffer） di-layer is found to be 300nm to yield a highly photo-catalytic property of the film without affecting the optical properties considerably. This multi-layer film can transmit light of above 75-85% in the visible spectrum （380 ≤ λ≤ 760 nm） and reflect radiation of above 90% in the infrared spectrum （ λ≥760 nm）. Such multi-layer coatings are strongly recommended not only as promising transparent heat mirrors but also as photo-catalytic films for architectural window coatings.