Supramolecular Nanowires from an Acceptor–Donor–Acceptor Conjugated Chromophore

Oligothiophene derivatives have been extensively studied as p-type semiconducting materials in organic electronics applications. This work reports the synthesis, self-assembly and photophysical properties of acceptor–donor–acceptor (A–D–A)-type oligothiophene derivatives by end-group engineering of quaterthiophene (QT) with naphthalene monoimide (NMI) chromophores that are further connected to a trialkoxy benzamide wedge. Conjugation to the NMI units reduces the HOMO–LUMO gap significantly, and consequently the absorption spectrum exhibits a bathochromic shift of about 50 nm compared with QT. Furthermore, extended H-bonding interactions among the amido groups of the peripheral wedges produce entangled fibrillar nanostructures and gelation in hydrocarbon solvents such as methylcyclohexane, wherein the A–D–A chromophore exhibits typical H-aggregation. On the contrary, the fact that the same chromophore, lacking only the amido units, does not produce gels or H-aggregates indicates strong impact of H-bonding on the self-assembly. Computational studies revealed the electronic properties of the chromophore and predicted the geometry of a dimer in the H-aggregate that reasonably matches with the experimental results. Bulk electrical conductivity measurements determined an excellent conductivity of 2.3×10⁻² S cm⁻¹ for the H-aggregated system (OT-1), which is two orders of magnitude higher than that of the same chromophore lacking the amido groups (OT-2).     

Influence of iodine on the electrical properties of magnesium phthalocyanines thin film devices

The influence of iodine on the electrical properties of sandwich structures of magnesium phthalocyanine (Mg Pc) thin films with gold and aluminium electrodes has been investigated. The various electrical properties and different electrical parameters of the iodine-doped Mg Pc thin film devices have been estimated and compared with the values of normal Mg Pc devices from the analysis of the current-voltage characteristics. Generally samples showed an asymmetric conductivity both under forward and reverse bias. From our study we found that iodine doped Mg Pc films showed an enhanced electrical conductivity of nearly ten times that of typical Mg Pc. At low voltages the films showed an ohmic conduction with a hole concentration of P₀ = 6.34 × 10¹⁸ m⁻³ and hole mobility μ = 9.16 × 10⁻⁵ m ² V⁻¹ s⁻¹, whereas at higher voltage levels the conduction is dominated by space charged limited conduction (SCLC) with a discrete trapping level of 1.33 × 10²² m⁻³ at 0.63 eV above the valance band edge. The ratio of the free charges to trapped charges (trapping factor) for the doped samples was found to be 1.07 × 10⁻⁷. Furthermore the reverse conduction mechanisms have also been investigated. From the current limitations in the reverse condition a strong rectifying behaviour was evident which was attributed to Poole-Frankel emission with a field-lowering coefficient of value 2.24 × 10⁻⁵ eV m^1/2 V^−1/2.     

Fabrication and Characterization of Monolithically Fused Wavelength-Independent 1 × 4 Couplers

A new method for the fabrication of a monolithic 1 × 4 single-mode fused coupler is described together with details of its performance in terms of coupling ratio, spectral response and polarization sensitivity. The fabricated device exhibits ultra-broadband performance with low polarization dependent loss. The coupling pattern exhibits identical coupling to all interacting fibers, enabling an easy control on fabrication parameters of the device.     

Consolidation of YBaCuO powders by shock loading

Superconducting oxide-copper monoliths have been fabricated by shock-wave loading using cylindrical and plane geometries. Bulk densities up to 96% T.D. have been obtained by varying detonation parameters. The superconducting properties, interface bonding and microstructure of the compacts have been evaluated.     

Preparation,Characterization, and X-Ray Structure Analysis of 1,4-Diazabicyclo-2,2,2-octane (DABCO) and Ammonium Cation with Tetrathiomolybdate Anion

The reaction of H₂S gas with an aqueous solution of ammonium heptamolybdate in the presence of 1,4-diazabicyclo-2,2,2-octane (DABCO) led to the formation of a red colored complex. The complex was recrystallized in hot water and characterized by elemental analysis and UV-Visible, FT-IR, and ¹H NMR spectroscopy. The single sharp peak in the ¹H NMR spectrum has revealed that all the methylene protons are equivalent due to the hydrogen resonating between the two nitrogens in the DABCO cation. The complex crystallizes in a cubic system with space group P2₁3, a = 10.9482(9) Å, α = 90°, V = 1325.3(7) ų, R ₃ = 0.0154, wR ₂ = 0.038, Z = 4. The structure consists of the tetrahedral tetrathiomolybdate anions, which form an extended three-dimensional network in the solid state involving Mo-S...H-N hydrogen bonding interactions with DABCO and the ammonium cation.Original Russian Text Copyright © 2004 by S. Pokhrel, K. S. Nagaraja, B. Varghese__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 945–949, September–October, 2004.     

Development and characterization of a solvent extraction-gas chromatographic/mass spectrometric method for the analysis of perfluorooctanesulfonamide compounds in solid matrices

A method utilizing solvent extraction and analysis by gas chromatography-positive chemical ionization mass spectrometry (SE-GC-PCIMS) was developed for the analysis of three neutral hydrophobic perfluorooctanesulfonamide compounds [perfluorooctanesulfonamide (PFOSA), N-ethyl perfluorooctanesulfonamide (N-EtPFOSA), and N,N-diethyl perfluorooctanesulfonamide (N,N-Et2PFOSA)]. These compounds are suspected metabolic precursors of perfluorooctane sulfonate. The SE-GC-PCI-MS method was used to analyze all three perfluorooctanesulfonamides in fast food, fish, and Arctic marine mammal liver samples. The SE-GC-PCI-MS method produced relatively higher recoveries of the analytes (averaging 83 +/- 6%, 84 +/- 9%, and 89 +/- 19% for N,N-Et2PFOSA, N-EtPFOSA, and PFOSA, respectively) with lower coefficients of variation, and less susceptibility to matrix effects, than ion pair extraction-liquid chromatography-tandem mass spectrometric methods. Method detection limits (MDLs) were 100, 120, and 250 pg/g for N,N-Et2PFOSA, N-EtPFOSA, and PFOSA, respectively. The three compounds were found at concentrations ranging from below the MDL to 22 ng/g wet weight in fast food, fish, and Arctic marine mammal liver samples.     

New allene synthesis via carbocupration-zinc carbenoid homologation and beta-elimination sequence

[reaction: see text] Polysubstituted propadienes are obtained in good to excellent yields by the consecutive carbocupration-homologation-beta-elimination reactions on the easily accessible alkynyl sulfoxides or sulfones. This one-pot reaction also allows the preparation of functionalized allenes.