Synthesis and electroluminescent properties of fluorene‐based copolymers containing electron‐withdrawing thiazole derivatives

We synthesized two fluorene‐based copolymers poly[(2,5‐bis(4‐hexylthiophen‐2‐yl)thiazolo[5,4‐day]thiazole‐5,5′‐diyl)‐alt‐(9,9′‐dioctylfluorene‐2,7‐diyl)] ( PF‐TTZT), and poly[(5,5′‐bis(4‐hexylthiophen‐2‐yl)‐2,2′‐bithiazole‐5,5′‐diyl)‐alt‐(9,9′‐dioctylfluorene‐2,7‐diyl)] (PF‐TBTT), which contain the electron‐withdrawing moieties, thiazolothiazole, and bithiazole, respectively. Through electrochemical studies, we found that these two polymers exhibit stable reversible oxidation and reduction behaviors. Moreover, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of PF‐TBTT are lower than those of PF‐TTZT, and the bandgap of PF‐TBTT is smaller than that of PF‐TTZT. Thus the bithiazole moiety in PF‐TBTT is more electron‐withdrawing than the thiazolothiazole moiety in PF‐TTZT. Light‐emitting devices with indium tin oxide (ITO)/poly(3,4‐ethylene dioxythiophene):poly(styrenesulfonate)(PEDOT)/polymer/bis(2‐methyl‐8‐quinolinato)‐4‐phenylphenolate aluminum (BAlq)/LiF/Al configurations were fabricated. The performance of the PF‐TBTT device was found to be almost three times better than that of the PF‐TTZT device, which is because electron injection from the cathode to PF‐TBTT is much easier than for PF‐TTZT. We also investigated the planarity and frontier orbitals of the electron donor‐acceptor (D‐A) moieties with computational calculations using ab initio Hartree–Fock with the split‐valence 6‐31G* basis set. These calculations show that TBTT has a more nonplanar structure than TTZT and that the bithiazole moiety is more electron‐withdrawing than thiazolothiazole. These calculations are in good agreement with the experimental results. © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7148–7161, 2008     

Mass distribution of fission fragments in the19F+197Au reaction

Mass distributions of fission fragments have been measured for the reaction of¹⁹F on¹⁹⁷Au as a function of scattering angle. The mean fragment mass is dependent on the scattering angle, the asymmetry increasing with increasing projectile energy.     

Extrapolation techniques for ill-conditioned linear systems

Summary. In this paper, the regularized solutions of an ill–conditioned system of linear equations are computed for several values of the regularization parameter . Then, these solutions are extrapolated at by various vector rational extrapolations techniques built for that purpose. These techniques are justified by an analysis of the regularized solutions based on the singular value decomposition and the generalized singular value decomposition. Numerical results illustrate the effectiveness of the procedures. Received June 23, 1997 / Revised version received October 24, 1997     

Surface restructuring of polymers

Time-dependent contact angle measurements are employed to follow the dynamics of surface modifications of various polymeric surfaces of different hydrophilicities. The equilibration of a hydrophilic polymer in a strong polar environment (such as water) induces an increase in the polarity of the surface; the subsequent exposure of the restructured solid to a nonpolar environment decreases the polarity of the surface. The dynamics of these processes depends on the history of the specimen. Various phenomena, such as surface restructuring by the reorientation of the buried polar or nonpolar moieties, water penetration into the polymer, and the reorganization of water in the neighborhood of the surface, are suggested to be responsible for the time evolution of the dynamic contact angles.     

The coefficient body of Bell representations of finitely connected planar domains

In this paper, we determine the homotopy type of the coefficient body of Bell representations of non-degenerate n-connected planar domains with n?3. Also, by considering the isomorphism classes of rational functions, we get the precise number of those corresponding to Bell representations with same set of critical values. Further, the case of those with the same set of critical points is discussed.     

Growth of multiwalled carbon nanotubes from acetylene over in situ formed Co nanoparticles on MgO support

The performance of Co catalysts supported on MgO at different Co loading (10%-75%) for the formation of carbon nanotubes through acetylene decomposition at 600 ^°C with H₂/C₂H₂ mixture for 1 h is investigated. The yield of MWNTs increases with an increase in Co loading (up to 50%). Starting from 1 g of catalyst precursor, about 8 g of MWNTs was obtained. The XRD patterns of catalyst precursor indicate the presence of cobalt in oxidic phase that eventually transformed into the catalytically active Co nanoparticles (12-18 nm) under the influence of acetylene and was responsible for the growth of coiled-like multi-walled CNTs as revealed by SEM and HRTEM images. It is suggested that bending in coil shaped MWNTs has the potential for functionalization for its biomedical applications.     

OEIC research in Korea

This paper presents a chronological overview of Korean activities in optoelectronics and optoelectronic integrated circuits (OEICs) undertaken mainly in university laboratories. OEIC transmitters and receivers for communications and semiconductor laser logic devices for optical switching and computing are briefly described.     

The insert of zinc oxide thin film in indium tin oxide anode for organic electroluminescence devices

Zinc oxide films were prepared by rf magnetron sputtering on glass substrates with designed ZnO target using high-purity of zinc oxide (99.99%) powder. Systematic study on dependence of target-to-substrate distance (D_ts) on structural, electrical and optical properties of the as-grown ZnO films was mainly investigated in this work. XRD showed that highly preferred ZnO crystal in the [0 0 1] direction was grown in parallel to the substrate, while the D_ts did not effect to the peak position of XRD. With decreasing D_ts, the growth rate is increased while the electrical resistivity as well as crystal size in the ZnO films was decreased. The XPS data showed that the O/Zn ratio in ZnO films was increased with increasing D_ts in the films. The as-grown ZnO films have an average transmittance of above 85% at the visible region. The optical band gap of the as-grown ZnO films was changed from 3.18 to 3.36 eV with D_ts. With decreasing D_ts, the electrical resistivity was decreased, while the growth rate was increased.A bilayer is used as an anode electrode for organic electroluminescent devices. The bilayer consists of an ultrathin ZnO layer adjacent to a hole-transporting layer and an Indium tin oxide (ITO) outerlayer. We tried to bring low the barrier between the devices as deposited ZnO films on ITO substrates. We fabricated the organic EL structure consisted of Al as a cathode, Al₂O₃ as an electro transport layer, Alq₃ as a luminously layer, TPD as a hole transport layer and ZnO (1 nm)/ITO (150 nm) as an anode. The result of this experiment was not good compared with the case of using ITO, nevertheless, at this structure we obtained the lowest turn-on voltage as the value of 19 V and the good brightness (6200 cd/m²) of the emission light from the devices. Then the quantum efficiency was to be 1.0%.     

Von klassischen Flächen zum Computer-Aided Geometric Design

Zusammenfassung. Der vorliegende Artikel beschreibt anhand einfacher Beispiele ein Verfahren, vorgegebene Zylinder oder Kegel durch ein weiteres Fl?chenstück (Teil einer sog.Dupinschen Zyklide) glatt zu verbinden (Blending). Zur L?sung werden Laguerregeometrie und Bézierdarstellung von Kurven verwendet. Ziel des Artikels ist es, grundlegende Ideen aus aktueller Forschung und Anwendung klassischer Geometrie darzustellen. Eingegangen am 07.01.1998 / Angenommen am 22.05.1998