Molecular ordering and 2D conductivity in ultrathin poly(3-hexylthiophene)/gold nanoparticle composite films

This paper reports the first comparison of the structure and electrical conductivity properties of spin cast (SC) and Langmuir-Schaeffer (LS) films of regioregular poly(3-hexylthiophene) (P3HT). In addition, the effect of incorporating highly monodisperse Au nanoparticles (NPs), with a core diameter of approximately 5 nm, into SC and LS P3HT films is described. A detailed picture of molecular organization in the films has been obtained using ultraviolet-visible absorption spectroscopy, atomic force microscopy, field-emission scanning electron microscopy, X-ray diffraction, and X-ray reflectivity. Film morphology was correlated with pseudo-two-dimensional conductivity measured using scanning electrochemical microscopy, with P3HT in the semiconducting regime. It was found that SC films, which were slightly thicker than those formed with the LS technique, exhibited greater organization. This resulted in an order of magnitude higher lateral conductivity for the SC films. Inclusion of Au NPs (50 wt %) into both SC and LS films resulted in the formation of uniform and relatively flat (rms roughness approximately 1 nm) composite films. Surprisingly, the addition of NPs did not disrupt the characteristic crystal structure found for the native P3HT films. The effect of Au NPs on film lateral conductivity was found to be determined by the distribution of Au NPs within the polymer, which varied significantly between SC and LS films. Whereas Au NPs aggregated into hexagonally packed clusters in SC films, NPs in LS films were predominantly uniformly distributed between the lamella bilayer. It was found that, while the inclusion of Au NPs caused the lateral conductivity to decrease in SC films, in LS films, the lateral conductivity increased by a factor of 2.     

X-band Electron Spin Relaxation Times for Four Aromatic Radicals in Fluid Solution and Comparison with Other Organic Radicals

X-band electron spin relaxation times of BDPA (1:1 α,γ-bisdiphenylene-β-phenylallyl), galvinoxyl 2,6-di-tert-butyl-α-(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-p-tolyloxy, DPPH (2,2-diphenyl-1-picrylhydrazyl) and thianthrene radicals in fluid solution were measured by electron spin echo and inversion recovery at ambient temperature. Tumbling correlation times are estimated to be in the range of 20–30 ps. In this fast tumbling regime T ₁ ~ T ₂. Relaxation times are compared with previously reported values for symmetrically substituted triarylmethyl, semiquinone, and nitroxide radicals. The concentration dependence of spin lattice relaxation for neutral BDPA in toluene is about 10³ times greater than for anionic trityl radicals in water. T ₁ decreases in the order carbon-center BDPA > galvinoxyl > DPPH > thianthrene. The dominant relaxation mechanisms are proposed to be a local mode for BDPA, spin rotation, local mode and modulation of anisotropic proton hyperfine coupling for galvinoxyl, modulation of anisotropic nitrogen hyperfine for DPPH, and spin rotation plus modulation of anisotropic proton hyperfine coupling for thianthrene.     

Behavior of water in contact with model hydrophobic cavities and tunnels and carbon nanotubes

By means of molecular dynamics simulations we analyze the behavior of water in contact with model hydrophobic cavities and tunnels. We study the hydration and filling propensity of cavities and tunnels carved in alkane monolayers and, for comparison, we also study single-walled carbon nanotubes of similar size. Our results will determine the dependence of the filling propensity as a function of cavity size while revealing the dynamical nature of the process with alternation of filled and dry states. Concerning the tunnels built across the monolayer, we shall show that the minimum diameter in order to get filled is about twice as large as that for the carbon nanotubes, thus evidencing a more hydrophobic behavior. The existence of water-water hydrogen bonds, a necessary condition for penetration, will also be made evident.     

A semiempirical molecular orbital calculation of borazine and some B-trifluoroborazines

A charge self-consistent semiempirical calculation has been performed on borazine and four fluoroborazines in which all the valence electrons of the molecules studied have been included. The results of the Mulliken population analyses are discussed in terms of the effect of fluorine bonded to boron and/or nitrogen. The correspondence between experiment and calculation for the orbital energies is also discussed.

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Zusammenfassung An Hand der Resultate ladungskonsistenter semi-empirischer Rechnungen für Borazin und vier Fluoroborazine unter Einbeziehung aller Valenzelektronen wird mittels Populationsanalyse die Frage diskutiert, wie sich die Bindung von Fluor an Bor und/oder Stickstoff auswirkt. Außerdem wird auf die Korrespondenz zwischen experimentellen Daten und Orbitalenergien eingegangen.

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Résumé Un calcul semi-empirique avec autocohérence des charges a été effectué sur le borazole et quatre fluoroborazoles avec introduction de tous les électrons de valence. Discussion des résultats de l'analyse de population de Mulliken en termes d'effet du fluor lié au bore et (ou) à l'azote. Discussion de la correspondance entre expérience et théorie pour les énergies orbitales.

     

Synthesis of nopol over MCM-41 catalysts

MCM-41 was found to be an active heterogeneous catalyst for the synthesis of nopol by the Prins condensation of beta-pinene and paraformaldehyde, but Sn-MCM-41 in which Sn has been grafted on MCM-41 by chemical vapor deposition is far more active and combines high efficiency and recyclability.     

Ultrafast photophysics of the isolated indole molecule

The relaxation dynamics of the isolated indole molecule has been tracked by femtosecond time-resolved ionization. The excitation region explored (283-243 nm) covers three excited states: the two ππ* L(b) and L(a) states, and the dark πσ* state with dissociative character. In the low energy region (λ > 273 nm) the transients collected reflect the absorption of the long living L(b) state. The L(a) state is met 1000-1500 cm(-1) above the L(b) origin, giving rise to an ultrafast lifetime of 40 fs caused by the internal conversion to the lower L(b) minimum through a conical intersection. An additional ~400 fs component, found at excitation wavelengths shorter than 263 nm, is ascribed to dynamics along the πσ* state, which is likely populated through coupling to the photoexcited L(a) state. The study provides a general view of the indole photophysics, which is driven by the interplay between these three excited surfaces and the ground state.     

Difluoro-boron-triaza-anthracene: a laser dye in the blue region. Theoretical simulation of alternative difluoro-boron-diaza-aromatic systems

The synthesis, photophysical and laser properties of a difluoro-boron-triaza-anthracene (BTAA) compound are analyzed in the present paper. The molecular structure of this dye is an anthracene-like core with N atoms at 4a, 9 and 10a positions where two of them (4a and 10a) are linked through a BF(2)-bridge group. This structure is reminiscent of aza-BODIPY dye with an s-indacene core, BODIPY being one of the most commonly used laser dye family in the Vis region. The main absorption and emission bands of the new dye are localized in the blue part of the Vis region of the electromagnetic radiation, a spectral region practically unexploited by the BODIPY chromophore. Moreover, the new dye presents a higher laser efficiency and photostability than other commercial laser dyes operating in the same spectral region. In order to look for new molecular structures with potential laser emission covering the whole Vis spectral region, the spectroscopic properties of other different chromophoric systems based on BF(2)-linking aromatic groups are theoretically simulated by quantum mechanical calculations.     

Immunoassay as an analytical tool in agricultural biotechnology

Immunoassays for biotechnology engineered proteins are used by AgBiotech companies at numerous points in product development and by feed and food suppliers for compliance and contractual purposes. Although AgBiotech companies use the technology during product development and seed production, other stakeholders from the food and feed supply chains, such as commodity, food, and feed companies, as well as third-party diagnostic testing companies, also rely on immunoassays for a number of purposes. The primary use of immunoassays is to verify the presence or absence of genetically modified (GM) material in a product or to quantify the amount of GM material present in a product. This article describes the fundamental elements of GM analysis using immunoassays and especially its application to the testing of grains. The 2 most commonly used formats are lateral flow devices (LFD) and plate-based enzyme-linked immunosorbent assays (ELISA). The main applications of both formats are discussed in general, and the benefits and drawbacks are discussed in detail. The document highlights the many areas to which attention must be paid in order to produce reliable test results. These include sample preparation, method validation, choice of appropriate reference materials, and biological and instrumental sources of error. The article also discusses issues related to the analysis of different matrixes and the effects they may have on the accuracy of the immunoassays.     

Synthesis of enantiopure allylamines by reductive alkylation of amino epoxides with organolithium reagents

[reaction: see text] Transformation of enantiopure (2R,1'S)-2-(1-aminoalkyl)epoxides 1 into the corresponding allylamines 2 is described. The opening of the epoxide ring with different organolithium compounds takes place with total selectivity and in high yields.     

Anion detection by fluorescent Zn(II) complexes of functionalized polyamine ligands

The Zn(2+) coordination chemistry and luminescent behavior of two ligands constituted by an open 1,4,7-triazaheptane chain functionalized at both ends with 2-picolyl units and either a methylnaphthyl (L1) or a dansyl (L2) fluorescent unit attached to the central amino nitrogen are reported. The fluorescent properties of the ZnL1(2+) and ZnL2(2+) complexes are then exploited toward detection of anions. L1 in the pH range of study has four protonation constants. The fluorescence emission from the naphthalene fluorophore is quenched either at low or at high pH values leading to an emissive pH window centered around pH = 5. In contrast, in L2 the fluorescence emission from the dansyl unit occurs only at basic pH values. In the case of L1, a red-shifted band appearing in the visible region was assigned to an exciplex emission involving the naphthalene and the tertiary amine of the polyamine chain. L1 forms Zn(2+) mononuclear complexes of ZnH(p)L1((p+2)+) stoichiometry with p = 1, 0, -1. Formation of the ZnL1(2+)species produces a strong enhancement of the L1 luminescence leading to an extended emissive pH window from pH = 5 to pH = 9. Addition of several anions to this last complex leads to a partial quenching effect. On the contrary, the fluorescence emission of L2 is partially quenched upon complexation with Zn(2+) in the same pH window (5 < pH < 9). The lower stability of ZnL2(2+) with respect to ZnL1(2+) suggests a lack of involvement of the sulfonamide group in the first coordination sphere. However, there is spectral evidence for an interesting photoinduced binding of the sulfonamide nitrogen to Zn(2+). While addition of diphosphate, triphosphate, citrate, and D,L-isocitrate to a solution of ZnL2(2+) restores the fluorescence emission of the system (lambda max ca. 600 nm), addition of phosphate, chloride, iodide, and cyanurate do not produce any significant change in fluorescence. Moreover, this system would permit one to differentiate diphosphate and triphosphate over citrate and d, l-isocitrate because the fluorescence enhancement observed upon addition of the first anions is much sharper. The ZnL2(2+) complex and its mixed complexes with diphosphate, triphosphate, citrate, and D,L-isocitrate have been characterized by (1)H, (31)P NMR, and Electrospray Mass Spectrometry.