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Absorption Measurements (absorption + measurement)
Kinds of Absorption Measurements Selected AbstractsPolymer Bonded Ferrite Materials as EMC ComponentsMATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 7 2003J. Töpfer Polymergebundene Ferrite; Ferritabsorber; Permeabilität; Dämpfung Abstract Polymer bonded ferrites composed of a mixture of Mn-Zn ferrites or Ni-Zn ferrites in a polymer binder (PE, PA) were prepared and tested as electromagnetic-wave absorbing materials. Test samples and cases were prepared by hot or injection molding. Permeability spectra show loss contributions in the frequency range 100-1000,MHz. Absorption measurements of injection molded polymer-ferrite cases display a 3-5,dB better attenuation characteristics compared to graphite-loaded polyamide housings. Polymer-gebundene Ferritwerkstoffe für EMV-Anwendungen Polymer-gebundene Ferritwerkstoffe auf der Basis von Ferrit (Mn-Zn oder Ni-Zn Ferrite) , Thermoplast Mischungen wurden präpariert und hinsichtlich ihrer Eignung zur Absorption elektromagnetischer Strahlung untersucht. Es wurden sowohl Testproben wie auch komplette Gehäusekomponenten durch Heißpressen oder Spritzgießen hergestellt. Die Permeabilitätsspektren weisen verlustbehaftete Komponenten im Frequenzbereich von 100-1000,MHz auf. Schirmdämpfungsmessungen an spritzgegossenen Gehäuseteilen zeigen eine um 3-5,dB bessere Dämpfung im Vergleich zu Graphit-gefüllten Polyamid-Gehäusen. [source] Infrared transient absorption spectra for excited transition of excitons and biexcitons in CuClPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2009Takaaki Yoshioka Abstract Infrared transient absorption (IRTA) spectra for excitons and biexcitons in CuCl bulk crystal have been measured by pump-probe spectroscopy. The IRTA peak energy of the exciton agrees with the transition energy between Rydberg 1s to 2p states reported in one- and two-photon absorption measurement. On the other hand, the IRTA peak energy of the biexcitons locates in energy higher than that of the excitons, which is reasonable by taking hydrogen molecule model into account. In addition, our results support the enhancement of the transition energy between 1s and 2p states in quantum dots compared to the bulk case. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth and characterization of undoped, Sr2+ -, and Mn2+ -doped ammonium tetrachlorozincateCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2005M. A. Gaffar Abstract Crystals of ammonium tetrachlorozincate (AZC) undoped and doped with Sr2+ or Mn2+ in different concentrations were grown by the slow evaporation method from an aqueous solution. The crystal morphology changed considerably by doping. The dopant concentration in the crystals was measured by the atomic absorption technique. Slight changes in the unit cell parameters of AZC after doping with Sr2+ - or Mn2+ have been detected. Optical absorption measurements indicated strong influence of Sr2+ and Mn2+ doping. The optical energy gap at room temperature decreased continuously with increasing Sr2+ and Mn2+ concentration but with two different rates. The dc conductivity was also measured as a function of temperature for the undoped and two samples doped with 0.144 Sr2+ and 0.191 Mn2+ and the results were compared. Positions possibly occupied by Sr2+ and Mn2+ cations in AZC lattice have been identified. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ultrasound-Assisted Synthesis of CuO Nanorods in a Neat Room-Temperature Ionic LiquidEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2009Tarek Alammar Abstract CuO nanorods were prepared via ultrasound-assisted synthesis in the room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide [C4mim][Tf2N] as a reaction medium. The structure and morphology of CuO nanorods were characterized with X-ray powder diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), vibrational and UV/Vis absorption spectroscopy. The synthesized CuO nanocrystals are of rod like shape with lengths from 30 to 100 nm and diameters of about 10 nm. Quantum size effects were observed as the bandgap of the CuO nanorods was determined to 2.41 eV from UV/Vis absorption measurements, which is significantly larger than the bulk value. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Experimental and Theoretical Evidence of ,-d Interactions in Supramolecular Assemblies Based on TTF-CH=CH-Py Ligands Tethered to Mo6Xi8 Octahedral Molybdenum Halide Cluster CoresEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2009Ganesan Prabusankar Abstract Synthesis, characterization, and physical properties of [Mo6Xi8(TTF-CH=CH-Py)a6]4+ supramolecular assemblies [TTF = tetrathiafulvalene; Py = pyridine; X = Cl (1), Br (2),I (3)] resulting from the reaction between [Mo6Xi8(OSO2CF3)6]2, cluster precursor and TTF-CH=CH-Py ligands were investigated. They are based on the association of the strongly delocalized metallic electron [Mo6Xi8]4+ cluster cores with six redox-active ,-conjugated TTF-CH=CH-Py terminal ligands attached to the Mo clusters through the pyridinyl group. Synergetic ,-d interactions between the organic ligands and the cluster core were experimentally evidenced by electrochemistry and absorption measurements, and corroborated by DFT calculations.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Design and Fabrication of Magnetically Functionalized Core/Shell Microspheres for Smart Drug DeliveryADVANCED FUNCTIONAL MATERIALS, Issue 2 2009Xiuqing Gong Abstract The fabrication of magnetically functionalized core/shell microspheres by using the microfluidic flow-focusing (MFF) approach is reported. The shell of each microsphere is embedded with magnetic nanoparticles, thereby enabling the microspheres to deform under an applied magnetic field. By encapsulating a drug, for example, aspirin, inside the microspheres, the drug release of the microspheres is enhanced under the compression,extension oscillations that are induced by an AC magnetic field. This active pumping mode of drug release can be controlled by varying the frequency and magnitude of the applied magnetic field as well as the time profile of the magnetic field. UV absorption measurements of cumulative aspirin release are carried out to determine the influence of these factors. The drug release behavior is found to be significantly different depending on whether the applied field varies sinusoidally or in a step-function manner with time. [source] Energy-Modulated Heterostructures Made with Conjugated Polymers for Directional Energy Transfer and Carrier Confinement,ADVANCED FUNCTIONAL MATERIALS, Issue 15 2007R. Favarim Abstract In this paper we demonstrate that multilayer structures with modulated bandgaps can be used for efficient energy transfer and carrier confinement inside a nanostructured film of a light-emitting polymer. The films were produced with the layer-by-layer technique (LbL) with a poly(p -phenylene vinylene) (PPV) precursor and a long chain dodecylbenzenesulfonate ion (DBS). DBS is incorporated selectively into the precursor chain, and with a rapid, low temperature conversion process (100,°C) superstructures with variable HOMO,LUMO gap could be formed along the deposition direction by changing the DBS concentration. Structures with different stair-type energy modulations were produced, which are thermally stable and reproducible, as demonstrated by UV-VIS. absorption measurements. Energy differences of up to 0.5,eV between the lowest and highest conjugated layers inside the stair structure could be achieved, which was sufficient to guide the excitation over long distances to the lower bandgap layer. [source] Stable Blue Emission from a Polyfluorene/Layered-Compound Guest/Host Nanocomposite,ADVANCED FUNCTIONAL MATERIALS, Issue 7 2006E. Aharon Abstract In this study a blue-light-emitting conjugated polymer, poly(9,9-dioctylfluorene), is confined to the interlayer space of inorganic, layered metal dichalcogenide materials, metallic MoS2, and semiconducting SnS2. The nanocomposites are prepared through Li intercalation into the inorganic compound, exfoliation, and restacking in the presence of the polymer. X-ray diffraction and optical absorption measurements indicate that a single conjugated polymer monolayer, with an overall extended planar morphology conformation, is isolated between the inorganic sheets, so that polymer aggregation or ,,, interchain interactions are significantly reduced. Photoluminescence (PL) measurements show that the appearance of the undesirable green emission observed in pristine polymer films is suppressed by incorporating the polymer into the inorganic matrix. The blue emission of the intercalated polymer is stable for extended periods of time, over two years, under ambient conditions. Furthermore, the green emission is absent in the PL spectra of nanocomposite films heated at 100,°C for 7,h in air with direct excitation of the keto defect. Finally, no green emission was observed in the electroluminescence spectrum of light-emitting devices fabricated with a polymer-intercalated SnS2 nanocomposite film. These results support the proposed hypothesis that fluorenone defects alone are insufficient to generate the green emission and that interchain interactions are also required. [source] Synthesis and characterization of polyacrylamides containing meso -2,3-dimercaptosuccinic acid end groupsADVANCES IN POLYMER TECHNOLOGY, Issue 1 2010Cemal Özero Abstract By using meso -2,3-dimercaptosuccinic acid-cerium(IV) sulfate and meso -2,3-dimercaptosuccinic acid-potassium permanganate redox systems, the polymerization reaction of acrylamide (AAm) monomer was examined in aqueous acidic medium at low temperatures. Water-soluble polyacrylamides bearing meso -2,3-dimercaptosuccinic acid end groups were synthesized using meso -2,3-dimercaptosuccinic acid as a reducing agent. The effects of parameters such as the molar ratio of acrylamide to initiator, temperature, polymerization time, and sulfuric acid concentration on the yields and molecular weights of polymers were investigated. The augmentation in initiator concentration resulted in a decrease in molecular weight but an increase in the yield of polymers. The increase in reaction temperature from 20 to 60°C led to a decrease in the yield from 56.80% to 20.58%. Ce(IV) and Mn(VII) ions are reduced to Ce(III) and Mn(II) ions in the polymerization reaction and the synthesized acrylamide polymers containing meso -2,3-dimercaptosuccinic acid end groups can absorb these ions at the end of the polymerization reaction. Ultraviolet-visible and atomic absorption measurements of polymer solutions were performed to indicate complexation between polyacrylamide and Ce(III) ions or Mn(II) ions. © 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:45,53, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20180 [source] Surface properties of poly(ethylene oxide)-based segmented block copolymers with monodisperse hard segmentsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2009D. Husken Abstract The surface properties of segmented block copolymers based on poly(ethylene oxide) (PEO) segments and monodisperse crystallizable tetra-amide segments were studied. The monodisperse crystallizable segments (T6T6T) were based on terephthalate (T) and hexamethylenediamine (6). Due to the crystallinity of T6T6T being high (, 85%), the amount of amorphous T6T6T dissolved in the polyether phase was limited. The length of the PEO segments was varied (between 600 and 4600 g/mol) and effect of extending the PEO segments with terephthalic groups was investigated. Studied was the hydrophilicity of the surface by contact angle measurements and of the bulk copolymers by water absorption measurements The results were compared with data of PEO-poly(butylene terephthalate) (PEO-PBT) copolymers. For a given hydrophilicity of the bulk copolymer, the surface hydrophilicity decreased in the order PEO-PBT, PEO-T6T6T, and (PEO-T)-T6T6T. The use of short monodisperse hard segments resulted in low contact angles, with a lowest observed value of , 29°. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Liquid Rb micrometric droplets confined in paraffin wax: an X-ray absorption spectroscopy studyJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001Simone De Panfilis We have performed high-quality X-ray absorption measurements on crystalline (c -Rb) and liquid (l -Rb) Rubidium in the range from 15 K to 320 K. Performing a consistent analysis that takes into account the contribution of the medium range structure, we observe that the l -Rb spectrum is compatible with pair correlation function g(r) previously determined by neutron diffraction experiments. Due to the micrometric size of the liquid droplets we were able to observe a slight undercooling down to 290 K. We were also able to study the details of the very strong multielectron excitations channels in terms of resonances, edges and shake-off features at proper theoretical energy values. [source] Preparation and characterization of pulse electrodeposited GaAs filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2006K. R. Murali Abstract GaAs is a III,V compound possessing high mobility and a direct band gap of 1.43 eV, making it a very suitable candidate for photovoltaic applications. Thin GaAs films were prepared by plating an aqueous solution containing GaCl3 and As2O3 at a pH of 2 and at room temperature. The current density was kept at 50 mA cm,2 and the duty cycle was varied in the range 10,50%. The films were deposited on titanium, nickel and tin oxide coated glass substrates. Films exhibited polycrystalline nature with peaks corresponding to single-phase GaAs. Optical absorption measurements indicated a direct band gap of 1.40 eV. Atomic force microscope measurements indicated uniform coverage with large crystallites for the films deposited at higher duty cycles. Photoelectrochemical cells were made using the films as photoelectrodes and graphite as counter electrode in 1 M polysulphide electrolyte. At 60 mW cm,2 illumination, an open-circuit voltage of 0.5 V and a short-circuit current density of 5.0 mA cm,2 were observed for the films deposited at a duty cycle of 50%. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Pressure dependence of the optical properties of wurtzite and rock-salt Zn1,xCoxO thin filmsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2007J. A. Sans Abstract In this paper we investigate the electronic structure of Zn1,xCoxO by means of optical absorption measurements under pressure. Thin films of Zn1,xCoxO with different Co content (from 1 to 30%) were prepared by pulsed laser deposition on mica substrates. Absorption spectra exhibit three main features that are clearly correlated to the Co content in the films: (i) absorption peaks in the infrared associated to crystal-field-split internal transitions in the Co 3d shell, with very small pressure coefficients due to their atomic character; (ii) a broad absorption band below the fundamental edge associated to charge transfer transitions, that exhibit relatively large pressure coefficients, indicating that the Co 3d final states must be strongly hybridized to the conduction band; and (iii) a blue-shifted fundamental absorption edge associated to band to band transitions with a pressure coefficient close to that of pure ZnO. In the up-stroke the transition pressure from wurtzite to rock-salt phase decrease almost linearly as the Co increases, from 9.5 GPa in pure ZnO to about 6.5 GPa for x = 30%. In the down-stroke pressure we observe a similar behavior, yielding a metastable rock-salt phase at room pressure, after a pressure cycle up to 15 GPa. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Light-induced neutralization of hydrogen shallow donors in zinc oxidePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2006N. H. Nickel Abstract Infrared absorption measurements of the O,H shallow donor complex in zinc oxide show that its vibrational mode is very sensitive to sub band-gap illumination. Upon illumination the intensity of the O,H vibrational line exhibits a pronounced decrease. This effect is completely reversible. Annealing the specimens at temperatures above 30 K restores the O,H vibrational line. The decrease and increase of the O,H absorption line is caused by a change of the infrared effective charge due to neutralization and ionization, respectively, of H shallow donors. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Far-infrared spectroscopy of shallow acceptors in semi-insulating GaAs: evidence for defect interactions with EL2PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2003H. Ch. Abstract Far-infrared FTIR absorption measurements are carried out at 10 K in order to assess the uncompensated fraction of shallow acceptors in semi-insulating GaAs after optical bleaching of EL2. In carbon-doped material a linear correlation of the G line at 122.3 cm,1 with the CAs concentration is found in the whole concentration range between 1 × 1014 and 2 × 1016 cm,3. In samples co-doped with zinc in the range around 1 × 1016 cm,3 and 1 to 2 × 1015 cm,3 carbon, both, ZnGa - and CAs -related far-infrared absorption lines are observed. Taking into consideration the Fermi level position after bleaching of EL2, it can be concluded that no other donors than EL2 are present above a total concentration of 1 × 1015 cm,3. In addition to the far-infrared measurements, the intracentre transition of EL2 (A1 , T2) at 1.0389 eV is studied. The results are compatible only with an increase of the total EL2 concentration with the shallow acceptor concentration. Possible mechanisms for the interaction between shallow- and deep-level defects are discussed. [source] Electrical properties and optical absorption in InN:In structuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008T. A. Komissarova Abstract Electrophysical and optical absorption measurements have been performed for conventional InN epilayers and InN:In composite structures grown by plasma-assisted molecular beam epitaxy. It is shown that intentional periodical introduction of In metallic inclusions into InN layers results in formation of inhomogeneous arrays of clusters. Their presence modifies the shape of absorption spectra. At the same time, significant amount of indium (up to 1/3 of a thickness) in these structures does not influence noticeably the carrier concentration and mobility. These parameters fall in the range of published data for the conventional InN layers. These finding can indicate that formation of In clusters in InN is a more frequent event than it is currently accepted. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Femtosecond transient absorption study of excitons in quasi-one-dimensional MX-chain compoundsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2006Y. Wada Abstract Two photon absorption spectra of [Pt(en)2][Pt(en)2Br2](SO4)2.6H2O have been measured by the femto-second transient absorption measurements. A two photon absorption band of an exciton with even parity has been found 0.8 eV above the one photon absorption band of an exciton with odd parity. The two photon absorption coefficient has been estimated at 1.5x102 cm/GW for pump energy of 1.56 eV and for probe energy of 1.95 eV at 100 K. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Plasma Modification of PDMS Microfluidic Devices for Control of Electroosmotic FlowPLASMA PROCESSES AND POLYMERS, Issue 4 2007Ina T. Martin Abstract Polydimethylsiloxane (PDMS) capillary electrophoresis microchips were modified using plasma-enhanced chemical vapor deposition (PECVD), resulting in modified electroosmotic flow (EOF) values. Octafluoropropane (C3F8) and acrylic acid (AA) plasmas were chosen as initial test systems for device modification. Argon plasma pretreatments were used to improve adhesion of the fluorocarbon (FC) and AA films. Contact angle measurements and X-ray photoelectron spectroscopy data demonstrated that the Ar/C3F8 plasma treatment of PDMS results in the deposition of a hydrophobic, crosslinked FC film, whereas the Ar/AA plasma treatment results in the deposition of a hydrophilic film with ionizable acid groups. The extent of plasma modification within the device channels was explored using scanning Auger microscopy and dye absorption measurements. EOF values were measured for plasma-treated chips as a function of pH, and aging studies were performed to determine the durability of the plasma treatments. Results show that EOF is decreased in Ar/C3F8 plasma-treated chips, and varies less with pH than untreated devices. Additionally, EOF measurements are constant for a minimum of 5 d. In contrast, EOF for Ar/AA plasma-treated devices is dependent on pH. EOF measurements of C3F8 and AA treated chips without the Ar pretreatment are less stable, particularly in the AA case. In addition to improving adhesion, the Ar plasma treatment results in a decreased hydrophobic dye absorption into the PDMS, which is attributed to the physical crosslinking of the polymer by the Ar plasma. [source] Reactive doping of PAni,CSA and its use in microwave absorbing materialsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 1 2009R. S. Biscaro Abstract Conductive coatings have been studied for static dissipation and as microwave absorbing materials. The doping process of polyaniline (PAni), which makes it conductive, is an important stage that determines the coating performance. For this purpose, polyaniline was doped by reactive processing in a torque rheometer using different molar ratios between PAni and acid (PAni:CSA) at three different temperatures (80, 90, and 100°C). Aqueous solution doping was also used in the ratio of 1:2 of PAni/CSA, with the aim to investigate the influence of different methods of PAni doping on its characteristics and, consequently, on the performance of coatings. Thermal analyses of the processed materials showed that PAni doped by both routes, reactive and solution processing, showed similar behaviors. X-ray diffraction analyses showed a semicrystalline structure for the PAni,CSA doped by reactive processing using high CSA concentrations and temperature. It was also observed that the doping process affects the dispersion of the components into the conductive coatings. Microwave absorption measurements (8,12,GHz) of PU-doped PAni blends showed the dependence of the doping type, the PAni,CSA concentration, and the mixing conditions of the components on the coating performance; it was found up to 99% of attenuation of the incident radiation for some composites in a narrow frequency range. The microwave absorption efficiency of the coating samples prepared by using the reactive doping process indicates the advantage of this methodology over solution doping. Moreover, the reactive process addresses the environmental requirements. Copyright © 2008 John Wiley & Sons, Ltd. [source] Supramolecular Architectures by Fullerene-Bridged Bis(permethyl-,-cyclodextrin)s with PorphyrinsCHEMISTRY - A EUROPEAN JOURNAL, Issue 42 2009Ying-Ming Zhang Abstract The Hirsch,Bingel reaction of bis{4-methyl[1,2,3]triazolyl}malonic ester-bridged bis(permethyl-,-cyclodextrin) 1 with C60 has led to the formation of a new fullerene-bridged bis(permethyl-,-cyclodextrin) 2, which has been comprehensively characterized by NMR spectroscopy, MALDI-MS, and elemental analysis. Taking advantage of the high affinity between 2 and 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (3) or [5,10,15,20-tetrakis(4-sulfonatophenyl)porphinato]zinc(II) (4), linear supramolecular architectures with a width of about 2,nm and a length ranging from hundreds of nanometers to micron dimension were conveniently constructed and fully investigated by transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM). Significantly, the photoinduced electron-transfer (PET) process between porphyrin and C60 moieties takes place within the 2,3 and 2,4 supramolecular architectures under light irradiation, leading to the highly efficient quenching of the porphyrin fluorescence. The PET process and the charge-separated state were investigated by means of fluorescence spectroscopy, fluorescence decay, cyclic voltammetry, and nanosecond transient absorption measurements. [source] ,-Substituted Terthiophene [2]RotaxanesCHEMISTRY - A EUROPEAN JOURNAL, Issue 19 2009Taichi Ikeda Dr. Abstract Towards polythiophene polyrotaxanes: The ,-substituted terthiophene [2]rotaxanes have been synthesized (see figure). Basic optical and electrochemical properties of the synthesized [2]rotaxanes are also reported. Two kinds of ,-substituted terthiophene [2]rotaxanes were synthesized using the host-guest pairs of the electron-deficient cyclophane cyclobis(paraquat- p -phenylene) (CBPQT4+) and the electron-rich terthiophenes with diethyleneglycol chains at the ,-position. One is made from the ,-position non-substituted terthiophene (3,T-,-Rx) and the other is made from the ,-dibromo-substituted terthiophene (3,TBr-,-Rx). The binding constants of the ,-substituted terthiophene threads were confirmed to be smaller than that of the ,-substituted terthiophene analogue. By UV/Vis absorption measurements, we confirmed the charge-transfer (CT) band in the visible region with an extinction coefficient of ,102 (M,1,cm,1). Strong, but not quantitative, quenching of the terthiophene fluorescence was confirmed for the [2]rotaxanes. Although the ,-substituted terthiophene thread was electrochemically polymerizable, the [2]rotaxane 3,T-,-Rx was not polymerizable. This result indicates that the interlocked CBPQT4+ macrocycle effectively suppresses the electrochemical polymerization of the terthiophene unit because electrostatic repulsive and steric effects of CBPQT4+ hinder the dimerization of the terthiophene radical cations. In the electrochemical measurement, we confirmed the shift of the first reduction peak towards less negative potential compared to free CBPQT4+ and the splitting of the second reduction peak. These electrochemical behaviors are similar to those observed for the highly-constrained [2]rotaxanes. The ,-substituted terthiophene [2]rotaxanes reported herein are important key compounds to prepare polythiophene polyrotaxanes. [source] The Structure-Controlling Solventless Synthesis and Optical Properties of Uniform Cu2S NanodisksCHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2008Yu-Biao Chen Dr. Abstract Uniform Cu2S nanodisks have been synthesized from a well-characterized layered copper thiolate precursor by structure-controlling solventless thermolysis at 200,220,°C under a N2 atmosphere. The development from small Cu2S nanoparticles (diameter ,3,nm) to nanodisks (diameter 8.3,nm) and then to faceted nanodisks (diameter 27.5,nm, thickness 12.7,nm) is accompanied by a continuous phase transition from metastable orthorhombic to monoclinic Cu2S, the ripening of small particles by aggregation, and finally the crystallization process. The growth of the nanoproduct is constrained by the crystal structure of the precursor and the in situ-generated thiol molecules. Such controlled anisotropic growth leads to a nearly constant thickness of faceted nanodisks with different diameters, which has been confirmed by TEM observations and optical absorption measurements. [source] Effect of Polarity and Structural Design on Molecular Photorefractive Properties of Heteroaromatic-Based Push,Pull DyesCHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2006Graziano Archetti Dr. Abstract A combined experimental (optical and electro-optical absorption measurements) and computational (ab initio RHF and DFT) approach has been used to investigate the molecular low- and high- Tg photorefractive (PR) performances of neutral and zwitterionic heteroaromatic dipolar chromophores in terms of structural and solvent-polarity effects. We have found that the nature of the building units (donor, acceptor, and spacer) and the polarity of the surrounding medium strongly affect all the relevant ground-state and nonlinear optical properties involved in the PR activity, that is, the dipole moment, the polarizability anisotropy, and first hyperpolarizability of the electronic ground-state. The variation of these properties is in turn transferred to molecular low- and high- Tg PR figures of merit. It is shown that PR molecular performance not only relies on a proper choice of structural components but varies by orders of magnitude as a function of the medium polarity, and this suggests that a combination of molecular design and host-matrix engineering is required for optimized performances of PR materials. [source] ,-Carbonyl Substituent Effect on the Lifetimes of Triplet 1,4-Biradicals from Norrish-Type-II ReactionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2006Xichen Cai Dr. Abstract Triplet 1,4-biradicals were generated by Norrish-Type-II hydrogen transfer from ,-heteroatom-substituted ,-branched butyrophenones 1,6 and detected by laser flash absorption measurements. For three oxy-substituted compounds 2,4 (R,=OH, OCOMe, OCOOEt) comparable lifetimes were determined in acetonitrile (roughly 1.5 ,s). In benzene, divergent trends were observed: for the hydroxy compound 2 a lower lifetime of 790 ns was determined, whereas for 3 and 4 the lifetimes increased to 4.9 ,s. Photolyses of the ,-amino-substituted compounds 1 and 6 resulted in transient species with significant lower lifetimes (for 1 160 ns in benzene and 450 ns in acetonitrile; for 6 <100 ns in both solvents). The mesyloxy substrate 5 undergoes rapid CO bond cleavage upon photolysis and no transient triplet species were detected. Computational (UB3,LYP/6,31G* and natural don orbital (NBO) analyses) results supported the assumption of a negative hyperconjugative interaction strongly stabilizing ,-oxy-substituted over ,-amino-substituted radicals. [source] Electrochemistry and Photophysics of Donor-Substituted Triarylboranes: Symmetry Breaking in Ground and Excited StateCHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2006Rainer Stahl Dipl.-Chem. Abstract We synthesized a series of amino substituted triarylboranes (TABs) 1,3 by copper(I)-catalyzed cross-coupling reactions. The title compounds were investigated by means of cyclic voltammetry (CV) and UV-visible absorption and fluorescence spectroscopy. Electrochemical oxidation of tris(4-carbazolyl-2,6-dimethylphenyl)borane (3) leads to the formation of an electroactive polymer film on the electrode surface. The charge-transfer (CT) absorption band of all three TABs shows a pronounced negative solvatochromism, while the emission is positively solvatochromic. By combining Jortner's theory, AM1 computations, and electrooptical absorption measurements (EOAM), this unexpected behavior was shown to be due to a dipole inversion upon S0,S1 excitation. Furthermore, polarized steady-state fluorescence spectroscopy and EOAM prove that the ground-state geometry of 3 is of lower symmetry than D3 and that the excitation energy can be transferred from one subchromophore to another within the lifetime of the excited state. Exciton-coupling theory was used to quantitatively analyze this excitation transfer. [source] Role of the Special Pair in the Charge-Separating Event in PhotosynthesisCHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2004Hidekane Ozeki Dr. Abstract We synthesized special-pair/electron-acceptor systems consisting of a complementary slipped cofacial dimer of imidazolyl-substituted zinc porphyrin, bearing pyromellitdiimide as the electron acceptor. In the case of the dimer, the first and second oxidation potentials were split into a total of four peaks in the differential pulse voltammetry measurement. Furthermore, the shift values of the first oxidation potentials obtained by changing the solvent polarity for the dimer were almost half of those observed for the monomer. These results indicate that the radical cation is delocalized over the whole , system of the dimer. Time-resolved transient absorption measurements revealed that, relative to the corresponding monomer, the dimer accelerated the charge separation rate, but decelerated the charge recombination rate. The smaller reorganization energy of the slipped cofacial dimer relative to that of the monomeric system demonstrates the significance of the special-pair arrangement for efficient charge separation in photosynthesis. [source] | ||||||||||||||||