High molecular weight mechanochromic spiropyran main chain copolymers via reproducible microwave-assisted Suzuki polycondensation

Suzuki–Miyaura polycondensation (SPC) is widely used to prepare a variety of copolymers for a broad range of applications. Although SPC protocols are often used in many instances, the limits of this method and issues of molecular weight reproducibility are not often looked at in detail. By using a spiropyran-based (SP) mechanochromic copolymer, we present an optimized protocol for the microwave-assisted synthesis of a mechanochromic, alternating copolymer P(SP-alt-C10) via SPC that allows the reproduction of molecular weight distributions. Several parameters such as microwave power, temperature, stoichiometry, and ligand are screened, leading to molecular weights up to Mw ∼ 174 kg mol−1. The process of optimization is guided by NMR end group analysis which shows that dehalogenation, oxidative deborylation and SP cleavage are the limiting factors that impede further increase of molar mass, while other classical side reactions such as protiodeborylation are not observed. Embossing films of P(SP-alt-C10) yields the colored merocyanine (MC) copolymer P(MC-alt-C10) that undergoes a thermally facilitated back reaction to P(SP-alt-C10). DFT suggests that the barrier of the SP → MC transition has two contributions, with the first one being related to the color change and the second one to internal bond reorganizations. The barrier height is 1.5 eV, which suggests that the ease of the thermally facilitated back reaction is either due to residual energy stored in the deformed polymer matrix, or arises from an MC isomer that is not in the thermodynamically most stable state

La importancia de la personalidad del traductor en los itinerarios de especialidad y en la selección de personal

Treball Final de Grau en Traducció i Interpretació. Codi: TI0983. Curs acadèmic: 2016/2017A pesar de que a simple vista no lo pueda parecer, la personalidad de los traductores influye mucho más de lo que se cree en el proceso traductor y en la toma de decisiones, como han puesto de manifiesto estudios empíricos. Para analizar cuáles son las diferencias individuales en la personalidad de los traductores en la elección del itinerario de especialidad, se ha llevado a cabo un estudio con los estudiantes de los cuatro itinerarios de traducción de la Universidad Jaume I, a fin de ver si podemos identificar los rasgos típicos de los estudiantes de cada itinerario. Además, dada la gran importancia de la personalidad en las tareas de traducción, también se ha entrevistado a responsables de tres agencias de traducción para ver si la personalidad de los traductores es un factor relevante a la hora de reclutar personal. Se ha comprobado así que sí hay algunos rasgos comunes en la personalidad de los estudiantes de cada itinerario y que realmente esta cuestión no es un factor relevante en las agencias de traducción, sino que se valora, sobre todo, el trabajo diario y la calidad de las pruebas de traducción

PCDTBT: From Polymer Photovoltaics to Light-Emitting Diodes by Side-Chain-Controlled Luminescence

Poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole) (PCDTBT) is a copolymer composed of alternating thiophene-benzothiadiazole-thiophene (TBT) and carbazole (Cbz) repeat units widely used for stable organic photovoltaics. However, the solubility of PCDTBT is limited, which decreases polymer yield and makes synthesis and purification tedious. Here, we introduce a strategy to increase both solubility and luminescence by the statistical incorporation of additional hexyl side chains at the TBT unit (hex-TBT). An increasing amount of hex-TBT as comonomer from 0 to 100% enhances solubility, leads to backbone torsion, and causes a blue-shift in the absorption and emission spectra. While photovoltaic performance of both PCDTBT:P3HT blends and PCDTBT:PC$_{71}$BM blends decreases with increasing content of hex-TBT due to weaker and blue-shifted absorption, the luminescence properties can be systematically improved. Both photo- and electroluminescence (PL and EL) quantum efficiencies increase with increasing hex-TBT content. We further demonstrate solution-processed red polymer light-emitting diodes based on fully hexylated PCDTBT showing an EL quantum efficiency enhancement of up to 7 times and 2 orders of magnitude enhancement of brightness compared to standard PCDTBT. Fully hexylated PCDTBT shows a peak external quantum efficiency of 1.1% and a peak brightness of 2500 cd/m2Financial support from the Fonds der Chemischen Industrie (FCI), the Research Innovation Fund of the University of Freiburg and the DFG (SPP1355) is greatly acknowledged. F.L. greatly acknowledges the EPSRC for funding. D.D. acknowledges the Department of Physics (University of Cambridge) and the KACST-Cambridge University Joint Centre of Excellence for support

Efficient and Stable Low Iridium Loaded Anodes for PEM Water Electrolysis Made Possible by Nanofiber Interlayers

Significant reduction of the precious metal catalyst loading is one of the key challenges for the commercialization of proton-exchange membrane water electrolyzers. In this work we combine IrOx nanofibers with a conventional nanoparticle-based IrOx anode catalyst layer. With this hybrid design we can reduce the iridium loading by more than 80% while maintaining performance. In spite of an ultralow overall catalyst loading of 0.2 mg(Ir)/cm(2), a cell with a hybrid layer shows similar performance compared to a state-of-the-art cell with a catalyst loading of 1.2 mg(Ir)/cm(2) and clearly outperforms identically loaded reference cells with pure IrOx nanoparticle and pure nanofiber anodes. The improved performance is attributed to a combination of good electric contact and high porosity of the IrOx nanofibers with high surface area of the IrOx nanoparticles. Besides the improved performance, the hybrid layer also shows better stability in a potential cycling and a 150 h constant current test compared to an identically loaded nanoparticle reference.BMBF, 05KI9VFA, Ultrahochauflösende Untersuchung des Wassertransports in alkalischen Brennstoff- und Elektrolysezellen mittels Neutronenradiographie und –Tomographie (NeutroSense

On the Effect of Prevalent Carbazole Homocoupling Defects on the Photovoltaic Performance of PCDTBT:PC17_{17}BM Solar Cells

The photophysical properties and solar cell performance of the classical donor–acceptor copolymer PCDTBT (poly($\textit{N}$-9′-heptadecanyl-2,7-carbazole-$\textit{alt}$ -5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole))) in relation to unintentionally formed main chain defects are investigated. Carbazole–carbazole homocouplings (Cbz hc) are found to significant extent in PCDTBT made with a variety of Suzuki polycondensation conditions. Cbz hc vary between 0 and 8 mol% depending on the synthetic protocol used, and are quantified by detailed nuclear magnetic resonance spectroscopy including model compounds, which allows to establish a calibration curve from optical spectroscopy. The results are corroborated by extended time-dependent density functional theory investigations on the structural, electronic, and optical properties of regularly alternating and homocoupled chains. The photovoltaic properties of PCDTBT:fullerene blend solar cells significantly depend on the Cbz hc content for constant molecular weight, whereby an increasing amount of Cbz hc leads to strongly decreased short circuit currents J$_{sc}$. With increasing Cbz hc content, J$_{sc}$decreases more strongly than the intensity of the low energy absorption band, suggesting that small losses in absorption cannot explain the decrease in J$_{sc}$ alone, rather than combined effects of a more localized LUMO level on the TBT unit and lower hole mobilities found in highly defective samples. Homocoupling-free PCDTBT with optimized molecular weight yields the highest efficiency up to 7.2% without extensive optimization.F.L., M.S., and R.F. gratefully acknowledge the EPSRC for funding. M.S. thanks the University of Freiburg (Innovationsfond Forschung) and the DFG for funding (SPP 1355). D.F. acknowledges the Alexander von Humboldt foundation for a postdoctoral research fellowship. A.D.Z.M. and C.M. thank the Swedish Research Council for funding

Total antioxidant activity and trace elements in human milk: the first 4 months of breast-feeding

The content of many nutrients in breast milk are dependent on the nutritional status of the lactating woman. This is particularly true for fat and water-soluble vitamins, some of which have antioxidant properties. The aim of the study entertained herein was to evaluate the changes in total antioxidant status of human milk during the first 4 months of lactation, and to correlate such changes with the contents in specific antioxidant oligoelements (Cu, Zn, Mn and Se). Milk samples were collected from (31) lactating women recruited at the Service of Obstetrics of the Hospital de São João in Porto, after 1, 4, 8, 12 and 16 weeks after birth. The total antioxidant status (TAS) of human milk was measured by the Randox® commercial kit and trace metals by ICP-MS (inductively coupled plasma-mass spectrometry). The results found for TAS and oligoelements under study show a decrease in the concentration of these parameters from 7 days to 4 months of breast-feeding and significant correlations (p < 0.05) were found between TAS and Cu, Zn and Se (not Mn). The decreases of Cu, Zn and Se were also correlated, but not proportional between them, suggesting diverse excretion mechanisms for all. Between primipara and multipara women, a significant difference was found only for Cu and Zn concentrations at 7 days of lactation, but not for the other metals or TAS. With respect to the mother’s age, no correlation was found, either for trace metal concentrations or TAS