Synthesis,Characterization, and Electronic Structures of Porphyrins Fused with Polycyclic Aromatic Ring Systems

A series of porphyrins fused with acenaphthylene, phenanthroline, and benzofluoranthene polycyclic aromatic rings were prepared by means of a 3+1 porphyrin synthesis approach and subsequent retro‐Diels–Alder reaction of bicyclo[2.2.2]octadiene‐fused precursors. Analysis of the magnetic circular dichroism spectra and the results of time‐dependent DFT calculations are used to identify the reasons for the trends observed in the wavelengths and relative intensities of the Q bands of the products. Michl's perimeter model is used as a conceptual framework to explain the changes in the relative energies of the frontier π‐molecular orbitals.     

Oxidative Annulation of Arenecarboxylic and Acrylic Acids with Alkynes under Ambient Conditions Catalyzed by an Electron‐Deficient Rhodium(III) Complex

It has been established that an electron‐deficient Cp^E rhodium(III) complex catalyzes the oxidative [4+2] annulation of substituted arenecarboxylic and acrylic acids with alkynes under ambient conditions (at RT–40 °C, under air) without using excess amounts of substrates to produce the corresponding substituted isocoumarins and α‐pyrones in high yields. Minor modification of reaction conditions depending on the coordination ability of alkynes realized the high efficiency.     

Lamellar structure in poly(ala-gly) determined by solid-state NMR and statistical mechanical calculations

Lamellar structure of poly(Ala-Gly) or (AG)n in the solid was examined using 13C solid-state NMR and statistical mechanical approaches. Two doubly labeled versions, [1-13C]Gly14[1-13C]Ala15- and [1-13C]Gly18[1-13C]Ala19 of (AG)15 were examined by two-dimensional (2D) 13C spin diffusion NMR in the solid state. In addition five doubly labeled [15N,13C]-versions of the same peptide, (AG) 15 and 15 versions labeled [3-13C] in each of the successive Ala residues were utilized for REDOR and 13C CP/MAS NMR measurements, respectively. The observed spin diffusion NMR spectra were consistent with a structure containing a combination of distorted beta-turns with a large distribution of the torsion angles and antiparallel beta-sheets. The relative proportion of the distorted beta-turn form was evaluated by examination of 13C CP/MAS NMR spectra of [3-13C]Ala-(AG)15. In addition, REDOR determinations showed five kinds of atomic distances between doubly labeled 13C and 15N nuclei which were also interpreted in terms of a combination of beta-sheets and beta-turns. Our statistical mechanical analysis is in excellent agreement with our Ala Cbeta 13C CP/MAS NMR data strongly suggesting that (AG)15 has a lamellar structure.     

Development of a cooled He*(23S) beam source for measurements of state-resolved collision energy dependence of Penning ionization cross sections: Evidence for a stereospecific attractive well around methyl group in CH3CN

A low-temperature discharge nozzle source with a liquid-N(2) circulator for He*(2(3)S) metastable atoms has been developed in order to obtain the state-resolved collision energy dependence of Penning ionization cross sections in a low collision energy range from 20 to 80 meV. By controlling the discharge condition, we have made it possible to measure the collision energy dependence of partial ionization cross sections (CEDPICS) for a well-studied system of CH(3)CN+He*(2(3)S) in a wide energy range from 20 to 350 meV. The anisotropic interaction potential energy surface for the present system was obtained starting from an ab initio model potential via an optimization procedure based on classical trajectory calculations for the observed CEDPICS. A dominant attractive well depth was found to be 423 meV (ca. 10 kcal/mol) at a distance of 3.20 A from the center of mass of CH(3)CN in the N-atom side along the CCN axis. In addition, a weak attractive well (ca. 0.9 kcal/mol) surrounding the methyl group (-CH(3)) has been found and ascribed to the interaction between an unoccupied molecular orbital of CH(3)CN and 2s atomic orbital of He*(2(3)S).     

Enhanced electrical properties of highly oriented poly(vinylidene fluoride) films prepared by solid‐state coextrusion

Oriented poly(vinylidene fluoride) (PVDF) films with β‐form crystals have been commonly prepared by cold drawing of a melt‐quenched film consisting of α‐form crystals. In this study, we have successfully produced highly oriented PVDF thin films (20 µm thick) with β‐crystals and a high crystallinity (55–76%), by solid‐state coextrusion of a gel film to eight times the original length at an established optimum extrusion temperature of 160°C, some 10°C below the melting temperature. The resultant drawn films had a highly oriented (orientation function f_c = 0.993) fibrous structure, showing high mechanical properties of an extensional elastic modulus of 8.3 GPa and tensile strength of 0.84 GPa, along the draw direction. Such highly oriented and crystalline films exhibited excellent ferroelectric and piezoelectric properties. The square hysteresis loop was significantly sharper than that of a conventional sample. The sharp switching transient yielded the remnant polarization P_r of 90 mC/m², and the electromechanical coupling factor k_t was 0.24 at room temperature. These values are about 1.5 times greater than those of a conventional β‐PVDF film. Thus, solid‐state coextrusion near the melting point was found to be a useful technique for the preparation of highly oriented and highly crystalline β‐PVDF films with superior mechanical and electrical properties. The morphology of the extrudate relevant to such properties is discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2549–2556, 1999     

Elastic modulus and thermal conductivity of ultradrawn polyethylene

The axial and transverse Young's modulus and thermal conductivity of gel and single crystal mat polyethylene with draw ratios λ = 1–350 have been measured from 160 to 360 K. The axial Young's modulus increases sharply with increasing λ, whereas the transverse modulus shows a slight decrease. The thermal conductivity exhibits a similar behavior. At λ = 350, the axial Young's modulus and thermal conductivity are, respectively, 20% and three times higher than those of steel. For this ultradrawn material both the magnitude and the temperature dependence of the axial Young's modulus are close to those of polyethylene crystal. The high values of the axial Young's modulus and thermal conductivity arise from the presence of a large percentage (∼85%) of long needle crystals. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3359–3367, 1999     

Regioselective hydrosilylations of propiolate esters with tris(trimethylsilyl)silane

Lewis acid and substituent dependency on the regioselectivity of hydrosilylation of propiolate esters 1a-c with tris(trimethylsilyl)silane (2a) was found. The reaction of methyl and ethyl propiolate esters and 2a without Lewis acid and in the presence of EtAlCl2 and Et2AlCl gave beta-silicon-substituted Z-alkenes 3 selectively. On the other hand, reaction in the presence of AlCl3 in dichloromethane gave alpha-silicon-substituted alkenes 4. In the case of trifluoroethyl propiolate ester 1c, reaction with aluminum chloride-based Lewis acids gave alpha-silicon-substituted alkenes 4 exclusively. Two competitive mechanisms, free-radical and ionic, are proposed as the source of the complementary regioselectivity displayed in these reactions. A transition state of the radical-forming step was obtained computationally. The reaction of various reactive acetylene substrates and 2a without Lewis acid and without solvent at room temperature gave beta-silicon-substituted Z-alkenes 3 selectively.