Acyclic diene metathesis polymerization of 2,5‐dialkyl‐1,4‐divinylbenzene with molybdenum or ruthenium catalysts: Factors affecting the precise synthesis of defect‐free,high‐molecular‐weight trans‐poly(p‐phenylene vinylene)s

Factors affecting the syntheses of high‐molecular‐weight poly(2,5‐dialkyl‐1,4‐phenylene vinylene) by the acyclic diene metathesis polymerization of 2,5‐dialkyl‐1,4‐divinylbenzenes [alkyl = n‐octyl ( 2 ) and 2‐ethylhexyl ( 3 )] with a molybdenum or ruthenium catalyst were explored. The polymerizations of 2 by Mo(N‐2,6‐Me₂C₆H₃) (CHMe₂ Ph)[OCMe(CF₃)₂]₂ at 25 °C was completed with both a high initial monomer concentration and reduced pressure, affording poly(p‐phenylene vinylene)s with low polydispersity index values (number‐average molecular weight = 3.3–3.65 × 10³ by gel permeation chromatography vs polystyrene standards, weight‐average molecular weight/number‐average molecular weight = 1.1–1.2), but the polymerization of 3 was not completed under the same conditions. The synthesis of structurally regular (all‐trans), defect‐free, high‐molecular‐weight 2‐ethylhexyl substituted poly(p‐phenylene vinylene)s [poly 3 ; degree of monomer repeating unit (DP_n) = ca. 16–70 by ¹H NMR] with unimodal molecular weight distributions (number‐average molecular weight = 8.30–36.3 × 10³ by gel permeation chromatography, weight‐average molecular weight/number‐average molecular weight = 1.6–2.1) and with defined polymer chain ends (as a vinyl group, ? CH?CH₂) was achieved when Ru(CHPh)(Cl)₂(IMesH₂)(PCy₃) or Ru(CH‐2‐OⁱPr‐C₆H₄)(Cl)₂(IMesH₂) [IMesH₂ = 1,3‐bis(2,4,6‐trimethylphenyl)‐2‐imidazolidinylidene] was employed as a catalyst at 50 °C. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6166–6177, 2005     

Effects of stretching on microstructures of polymer-immobilized non-close-packed colloidal crystalline array

Non-close-packed silica colloidal crystalline array was immobilized by polymer, and effects of stretching on the change of the optical properties and microstructure of the colloidal crystalline arrays have been demonstrated. The immobilization was a two-step polymerization process: the first step was with hydrophilic polyethylene glycol acrylate (PEGA) polymer gel, and the second step was with 2-hydroxyethyl acrylate polymer matrix. The structure of the three-dimensional array was maintained during the immobilizing process with lock in periodic order. The peak wavelength of Bragg diffraction of the polymer-immobilized colloidal crystalline array shifted to shorter wavelength with stretching. The peak shift was caused by the compression of the polymer proportional to the stretching ratio, and the compression was homogeneous throughout the polymer-immobilized colloidal crystalline arrays. These results show that by using polymer-immobilized non-close-packed colloidal crystalline array, mechanically tunable photonic crystals can be realized, and they open the possibility of tuning the microstructure of colloidal crystalline array for photonic crystal.     

11B solid-state NMR investigation of the rhamnogalacturonan II-borate complex in plant cell walls.

The boron in plant cell walls, which is water-insoluble and in the solid state, is solubilized by pectinase digestion to give a dimeric rhamnogalacturonan II-borate (dRG-II-B) complex. To clarify the nondestructive structure of boron present in plant cell walls (as represented by sugar beet fiber), we performed 192- and 96-MHz 11B solid state NMR measurements. The use of a high field magnet frequency of 192-MHz enabled us to observe 11B isotropic chemical shifts at -9.7 and -9.6 ppm for dRG-II-B and sugar beet fiber in the solid state, respectively, demonstrating that the boron in isolated dRG-II-B and in plant cell walls is present as a borate-diol ester (1:2). The observation of the magnetic field dependence of the chemical shift and lineshape for the borate-diol ester (1:2) by quadrupolar interaction suggested that the borate complex had a distorted tetrahedral boron structure.     

High-dynamic range pulse-contrast measurements of a broadband optical parametric chirped-pulse amplifier

We report on the pulse contrast-ratio characterization of a few-cycle 0.2 TW optical parametric chirped pulse amplifier system operating at 20 Hz. A specially designed third-order correlator was used to characterize and optimize the contrast of the system. We demonstrate that the pulse contrast depends much more on the temporal overlap between the pump and the seed pulse than the shape of the amplified spectrum. The best amplified pulse contrast-ratio was 10^-4 at Δt=±25 ps and >10^-9 at Δt=±150 ps delays. PACS 42.65.Vj; 42.65.Re     

Synthesis of arylboronates via Cp*RuCl-catalyzed cycloaddition of alkynylboronates

In the presence of 5-10 mol% Cp*RuCl(cod), 1,6- and 1,7-diynes were allowed to react with an ethynylboronate at ambient temperature to give rise to bicyclic arylboronates in 64-93% isolated yields. 1,6-Diynes bearing a boronate terminal also underwent cycloaddition with monoalkynes to give the corresponding bicyclic arylboronates.     

Photochemistry and photocuring properties of thiol‐substituted α‐aminoalkylphenone as radical photoinitiator

Thiol‐substituted α‐aminoalkylphenone was newly developed as a radical photoinitiator. Introduction of the thiol group drastically improved photosensitivity in an alkaline developable resist formulation composed of a prepolymer and a multifunctional acrylate monomer. The improvement in the photocuring speed was explained by a mechanism based on chain transfer reaction of the thiol group. Time‐resolved electron spin resonance (ESR) spectroscopy indicated that the thiol group attached to the chromophore does not influence the photochemical process to generate primary radicals. The photoinitiation of α‐aminoalkylphenone can be spectrally sensitized by 2,4‐diethylthioxanthone (DETX). However, thiol‐substituted α‐aminoalkylphenone showed smaller spectral sensitization than the corresponding compound without a thiol group. Time resolved laser flash photolysis indicated that the rate constant of the quenching of the triplet state of DETX by thiol‐substituted α‐aminoalkylphenone is twice as large as that by the corresponding one without a thiol group. This suggests that, besides energy transfer from DETX in the excited triplet state to the α‐aminoalkylphenone, the thiol group quenches the excited triplet state of DETX via charge transfer and/or hydrogen transfer, as supported by the ESR analysis using a spin trapping technique, and lowers the efficiency of the spectral sensitization effect. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1684–1695, 2005     

Photoluminescence inner core excitation in semiconductor quantum structures

We introduce a photoluminescence inner core excitation (PLICE) for the studies of semiconductor quantum structures. This novel method, in which we use synchrotron radiation as tunable excitation source, is expected to facilitate us to obtain electronic and compositional information about buried quantum structures. Here we report experimental results on quantum dots (QDs) and quantum wires (QWRs), in order to demonstrate potential applicability of the method to the semiconductor nanostructure studies.     

双奇核中πi13/2 νi13/22－准粒子转动带旋称反转研究

利用重离子熔合蒸发反应和在束γ谱学实验方法研究了双奇核^176,178Ir和¹⁸²Au的高自旋态结构,在这3个双奇核中观测到了基于πi_13/2 νi_13/2准粒子组态下的转动带.以能级间隔系统学为判据,对¹⁸⁴Au核中πi_13/2 νi_13/2转动带能级自旋进行了指定.指出^176,178Ir和^182,184Au 4个双奇核的πi_13/2 νi_13/2转动带在低自旋区均出现旋称反转.对πi_13/2 νi_13/2转动带旋称反转现象进行了定性的讨论.用推转壳模型对πh_9/2 νi_13/2带和πi_13/2 νi_13/2带能级结构进行了理论研究,发现当采用形变和对力自洽计算后,从理论上可以定性地解释两个半退耦带出现的旋称反转现象.