Luminescence Properties of New Fused Benzothiophene Derivatives and Their Conductive Oligomers Structural and Solvent Effects

The structural and solvent effects on the electronic absorption and fluorescence spectra, and fluorescence quantum yields, of four new fused benzothiophene derivatives, including benzothieno[3,2b]-thiophene (BTT), benzothieno[3,2-b]benzothiophene (BTBT), 6-methoxy[1]benzothieno[3,2b]-thiophene (MeOBTT), and benzothieno[3,2-b]indole (BTI) were investigated at 295 K. The luminescence properties of the corresponding conductive oligomers, poly(BTT) and poly (MeOBTT), electrosynthesized in acetonitrile, were also studied. Satisfactory McRae, Suppan, and Kawski-Chamma-Viallet solvatochromic correlations were established for the four monomers in most solvents. A weak negative solvatochromic behavior was found for these compounds, indicating that their dipole moments are slightly lower in the excited singlet state than in the ground state. Kamlet-Abboud-Taft multiparametric correlations were also obtained for absorption and fluorescence wave numbers and quantum yields, demonstrating the existence of specific solute-solvent interactions. In the case of the oligomers, important red-shifts of the fluorescence emission maxima ( 90–110 nm) relative to the corresponding monomers were observed, which shows the extent of conjugated segments in the oligomer chains.     

Small-angle X-ray scattering study of liquid crystalline polycarbonates based on α-methyl stilbene mesogen and methylene-containing flexible spacer

Crystallization and melting behavior are studied by small-angle X-ray scattering (SAXS) for a series of recently synthesized monotropic liquid crystalline polycarbonates based on α-methyl stilbene mesogen and methylene flexible spacer. The one-dimensional electron density correlation function is used to obtain long period, crystal thickness, and linear crystallinity from the Lorentz-corrected SAXS intensity. Changes in these parameters during nonisothermal crystallization and melting are explained by a model of dual crystal populations. The primary crystals form first using the liquid crystalline phase as crystal nuclei, while smaller and less perfect crystals form later from the isotropic phase at low temperature. The results of the real-time SAXS study of isothermal crystallization also support the view that the nematic phase serves as crystal nuclei for fast crystallization. An odd-even effect in crystal thickness and linear crystallinity is observed in all the SAXS experiments mentioned above. The results of this study and our complementary wide-angle X-ray scattering (WAXS) investigation show clearly that the difference in the position of the neighboring carbonate dipoles on a chain affects structural organization both at the unit cell level and at the level of the crystal in these monotropic LCPs. © 1995 John Wiley & Sons, Inc.     

Development of an analytical microsystem for organic gas detection based on surface acoustic wave resonators

Modified Surface Acoustic Wave (SAW) devices can be used as highly sensitive detectors for gases: coated with a selective sorptive layer, they serve as a frequency determining element of an oscillator circuit. To perform a quantitative analysis of organic gas mixtures with polymer coatings as sensitive membranes, it is necessary to use an array of several SAW sensors with sensitivities towards various gaseous components and a subsequent pattern recognition of the sensor responses. An automatic working, self purging and compact analytical microsystem has been developed for organic gas detection. As the central component it contains an array of nine commercially available SAW resonators working at frequency of 433.92 MHz. Eight sensor oscillators, one common reference oscillator for temperature compensation and circuits for frequency mixing are mounted within a compact radial housing (diameter 108 mm). A selection of polymers has been made to detect a broad variety of gaseous organic analytes. Of particular interest have been hydrocarbons, halogenated hydrocarbons and aromatic compounds. Initial experiments with these analytes have been carried out to proof the selection and to optimize the combination of polymer coatings. With the compact sensor configuration a very fast response time in the range of seconds is obtained for qualitative determination of the analytes.Dedicated to Professor Dr. Dr. h.c. mult. J. F. K. Huber on the occasion of his 70th birthday     

A canonical partition theorem for equivalence relations on Zt

A canonical version of the multidimensional version of van der Waerden's theorem on arithmetic progressions is proved.     

Determination of sulfur and moisture in coal using capture gamma-rays

Samples of coal weighing approximately 200 g placed in a collimated beam of neutrons from the thermal column of the Ames Laboratory Research Reactor produce capture gamma-rays which can be used for the determination of sulfur in the presence of iron, a potential source of interference. Spectra from NaI(Tl) detectors were used with the help of Ge(Li) spectra to locate interferences. Corrections for iron interference was made by the use of a higher energy iron peak. A linear relation was found between the area of the hydrogen capture peak at 2.23 MeV and the amount of water added to coal.     

CHEMILUMINESCENCE QUENCHING TERMS

Abstract— A methodology for the determination of chemiluminescence quenching terms is given. By using the oxidation of tetrakis(dimethylamino)ethylene as an example, it is shown how the nature and magnitude of the quenching terms help to elucidate the reaction mechanism, or how ignoring them can lead to false impressions. It is shown that chemiluminescence quenching effects need not be the same as those for photoluminescence of the same electronically excited species.     

Canonical partition theorems for parameter sets

A canonical (i.e., unrestricted) version of the partition theorem for k-parameter sets of Graham and Rothschild (Trans. Amer. Math. Soc.159 (1971), 257–291) is proven. Some applications, e.g., canonical versions, of the Rado-Folkman-Sanders theorem and of the partition theorem for finite Boolean algebras are given. Also the Erdös-Rado canonization theorem (J. London Math. Soc.25 (1950), 249–255) turns out to be an immediate corollary.     

Direct observation of azimuthal correlations between DNA in hydrated aggregates

This study revisits the classical x-ray diffraction patterns from hydrated, noncrystalline fibers originally used to establish the helical structure of DNA. We argue that changes in these diffraction patterns with DNA packing density reveal strong azimuthally dependent interactions between adjacent molecules up to approximately 40 A interaxial or approximately 20 A surface-to-surface separations. These interactions appear to force significant torsional "straightening" of DNA and strong azimuthal alignment of nearest neighbor molecules. The results are in good agreement with the predictions of recent theoretical models relating DNA-DNA interactions to the helical symmetry of their surface charge patterns.     

Analysis of HRTEM images for carbon nanostructure quantification

Image processing algorithms have been developed to extract fringe length, tortuosity and separation from high resolution transmission electron microscopy images. To validate the separation algorithm, a comparison is made between the image-based fringe separation and that obtained by analysis of X-ray diffraction data for a progressively heat-treated carbon black. Agreement is favorable. To illustrate the utility of the analysis parameters for a range of carbon nanostructures, analysis is applied to a series of pyrolytically prepared carbon soots – qualitatively described as containing amorphous, graphitic or fullerenic nanostructure. For all processing, the intermediate image, in the form of a skeletonized binary image of the original high resolution transmission electron micrograph, is shown and found to accurately reflect the nanostructural organization within the carbon as visually observed. Statistical results for each analysis parameter, extracted from the binary images, are presented in the form of histograms and quantitatively distinguish the different carbon nanostructures.