Electrochromic properties of poly(alkoxy-terthiophenes): an experimental and theoretical investigation

Much effort has been made to synthesize novel compounds and enhance the optical properties of poly(terthiophenes). The electrochromic properties of poly(4,4′′-dimetoxy-3′-methyl-2′-5′,2′′-terthiophene) (PDMMT) and poly(4,4′′-dipentoxy-3′-methyl-2′-5′,2′′-terthiophene) (PDPMT) have been studied focusing on the differences in the alkoxy-group length. Theoretical calculations were employed to elucidate the structural and thermodynamic stability of the monomers and dimmers. The results showed that in this type of thiophenes large alkoxy chains assist positive charge dispersion through hyperconjugative effect. Thus, PDPMT is thermodynamically more stable than PDMMT in the oxidized state, leading to better electrochromic stability and optical memory.     

A model of polyelectrolyte conductance in moist solvents as a basis of water sensors

The conductance of interpenetrated polymer networks (IPNs) containing quaternary amino groups was studied in cyclohexane, toluene, ethyl ether, ethyl acetate, and tetrahydrofurane as a function of water content by electrochemical impedance spectroscopy. IPNs were then used as sensitive materials to detect water traces in organic solvents with promising results for the construction of a moisture sensor. The detection onset for water concentration increased with the dielectric constant of the solvent. Different IPN-based sensors in the same solvent showed a detection limit at lower water concentration if their characteristic plot [conductance/relative humidity (RH%) in air] was shifted toward lower RH%. This suggests that the composition of this class of polymers can be tuned to achieve the best performance for each solvent.     

Columnar Liquid‐Crystalline Dinaphthoperylenetetracarboxdiimides

Although the double Friedel–Crafts acylation of arenes with ethyl chloroglyoxylate is hindered by the strongly deactivating effect of the first‐entering glyoxylic substituent, the double reaction is successful with the reactive arene perylene under long reaction times and with concomitant ester hydrolysis. The reaction is regiospecific, giving the 3,9‐regioisomer exclusively. This perylenylenediglyoxylic acid is condensed first with o‐bromophenylacetic acid and then with α‐branched alkylamines to yield the title compounds. Whilst the corresponding tetraalkyl esters only show monotropic mesophases, these diimides show enantiotropic columnar mesophases that can be maintained at room temperature if racemically branched alkyl chains of moderate size are used. A palladium‐induced C?C bond migration during the build‐up of the arene system leads to an isomeric side product of reduced symmetry that can be isolated by aggregation‐controlled chromatographic separation. The HOMO and LUMO energies of the title compounds are considerably higher than those of established perylenetetracarboxdiimides.     

Low coercive field and conducting nanocomposite formed by Fe3O4 and poly(thiophene)

Magnetite and poly(thiophene) composites have been produced by in situ monomer oxidation. Fourier transform infrared (FTIR) and X-ray diffraction (XRD) confirmed the presence of Fe₃O₄ as particle agglomerates ranging from 15 to ca. 54 nm in size. Transmission electron micrographs (TEMs) revealed a face-to-face structure in both the pure magnetite and the nanocomposite. Typical superparamagnetic (ferrimagnetic) curves have been observed, whereas the relatively weak magnetic field employed in measurement, 200 Oe, was sufficient to split the curves completely. Zero field cooling (ZFC) and field cooling (FC) curves coincide only above room temperature, indicating that the characteristic blocking temperature (T_B) for superparamagnetic particles in this assembly is above room temperature.     

Time-domain approach to parametric conversion: A comparative study on the impact of numerical dispersion

Numerical integration schemes of time-domain Maxwell equations in optical dispersive and nonlinear media are considered. In this context, we study quantitatively the impact of numerical dispersion on a typical nonlinear parametric conversion process, comparing the widely used finite difference (FDTD) approach and pseudo-spectral (PSTD) methods. Our results show that, unless using very dense grid, only fourth-order PSTD gives results in good quantitative agreement with standard coupled-mode theory.     

Spectroscopic properties of polycarbonate and poly(methyl methacrylate) blends doped with europium (III) acetylacetonate

Spectroscopic properties of blends formed by bisphenol-A polycarbonate (PC) and poly(methyl methacrylate) (PMMA) doped with Europium (III) acetylacetonate [Eu(acac)₃], have been studied by photoacoustic spectroscopy (PAS) and photoluminescent (PL) spectroscopy. Emission and excitation spectra, excited state decay times, and quantum efficiency have been evaluated as well. PAS studies evidenced chemical interactions between the Europium complex and the PC/PMMA blend, which presented typical percolation threshold behavior regarding the Eu³⁺ content. PL spectra evidenced the photoluminescence of the Eu³⁺ incorporated into the blend. Photoluminescence property enhancement was observed for the composite in comparison with the precursor compound. Optimized emission quantum efficiency was observed for the 60/40 blend doped with 2% and 4% Europium (III) acetylacetonate.     

Thiophene-based bent-shaped luminescent liquid crystals: synthesis and characterisation

Five new bent-shaped compounds based on the 2,5-disubstituted thiophene central core were successfully synthesised. The lengths of the rigid centres as well as the degree of conjugation were varied by coupling benzene, naphthalene and biphenyl systems to the thiophene through Sonogashira cross-coupling. The thermal, mesomorphic and optical properties of these variants were determined. Compounds 5a,b and 8a displayed liquid-crystalline smectic and nematic mesophases. Strong blue fluorescence was observed for the final compounds.     

Chebyshev type inequality for Choquet integral and comonotonicity

We supply a Chebyshev type inequality for Choquet integral and link this inequality with comonotonicity.     

New liquid crystals derived from thiophene connected to the 1,2,4-oxadiazole heterocycle

In this study, eight new compounds derived from thiophene were synthesised and characterised. The four symmetrical compounds contain two heterocyclic 1,2,4- oxadiazole on each side of the 2,5-disubstituted thiophene, and the four non-symmetrical compounds contain alkyne groups as a spacer replacing one of these heterocycles. Some of the compounds presented liquid crystalline properties with smectic and nematic mesophases. The non-symmetrical compounds presented low emission of blue light.