Synthesis and photophysical properties of dinaphtho[2,3-b:2′,3′-i]dihydrophenazine derivatives

A dinaphtho[2,3-b:2′,3′-i]dihydrophenazine (DNP) derivative was synthesized by Buchwald-Hartwig cross-coupling, and its electronic spectrum was compared with that of dinaphtho[b,i]dihydrophenazine-5,18-dione (DNP-dione) as an anthraquinone analog. An absorption band of DNP is attributed to extension of π-conjugation over the entire molecule via the N atom. DNP-dione showed a broad absorption band in the range 450–490?nm due to intramolecular charge-transfer interactions. Additionally, the absolute fluorescence quantum yield of DNP was larger than that of DNP-dione. DNP-dione exhibited reversible oxidation peaks and a similar oxidation potential to DNP, since there are very weak electronic interactions between the anthracene and anthraquinone units across the N atoms with the 4-octyloxyphenyl substituent.     

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     

Dansyl-Modified γ-Cyclodextrin as a fluorescent sensor for molecular recognition

The crystal structure of thiamine iodide sesquihydrate has been determined by X-ray diffraction methods as a host-guest model for coenzyme-substrate interactions. The asymmetric unit contains two chemical units. Both the thiamine molecules A and B, which are crystallographically independent, assume the usualF conformation and have a disordered hydroxyethyl side chain. An iodide anion (or a water molecule) bridges the pyrimidine and thiazolium rings of molecule A (or B) by forming a hydrogen bond with the amino group and an electrostatic contact with the thiazolium ring to stabilize the molecular conformation. In the crystal the thiamine molecules self-associate to form a pipe-like polymeric structure, in which four thiamine hosts surround an iodide guest and hold it through C(2)-H...I hydrogen bonds and thiazolium...I electrostatic interactions. Crystal data: C₁₂H₁₇N₄OS⁺·I^– · 1.5 H₂O, monoclinic,P2₁/c, a=12.585(2), b=25.303(5), c=12.030(2) Å, =115.15(1)°,V=3468(1) ų,Z=8,D _c=1.606 g cm^–3,R=0.045 for 3328 observed reflections. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP. 82156 (13 pages).     

Total synthesis of kehokorins A and B

The total synthesis of a dibenzofuran rhamnoside, kehokorin A, and its aglycone, kehokorin B, was achieved via a route including Suzuki-Miyaura cross-coupling followed by Ullmann ether synthesis to form a dibenzofuran, stepwise bromination at C7 of the dibenzofuran, a second Suzuki-Miyaura cross-coupling to install a 4-methoxyphenyl group at C7, and rhamnosylation.     

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     

Solute distribution coupled with laminar flow in wide-bore capillaries: what can be separated without chemical or physical fields?

Solute diffusion coupled with an orthogonal laminar flow has been systematically studied with wide-bore capillaries to establish its limitations and reveal its potentials as separation methodology requiring neither chemical nor physical interactions. Simulations based on the advection-diffusion equation in a cylindrical coordinate system indicate several important features of this potentially useful method: (1) if a solute diffuses over the entire cross-section of the capillary before it is eluted from the capillary, it behaves as a diffusive solute and gives a Gaussian-shaped peak (diffusion peak) having an apex at the traveling time of the average flow; (2) when a solute is poorly (or not) diffusive, a new peak appears with an apex at the elution time of the maximum flow (non-diffusion peak); (3) these two peaks are simultaneously detected for intermediately diffusive solutes; (4) the transformation from the diffusion to non-diffusion peak occurs when the solute diffuses over the distance 0.86 times as large as the capillary radius before it leaves the capillary. These results of simulations are consistent with experimental results for selected solutes having various diffusivities. This method has proved useful particularly for the evaluation of diffusion coefficients of poorly diffusive solutes. Separation of PS particles having different sizes is also attempted.     

Two unstable oscillations in the multimode laser with modulated inversion

We present comprehensive results of numerical studies on the dynamical properties of a multimode ring laser under modulation of the population inversion in the bad-cavity condition. Incoherent properties of unstable oscillations in this system are investigated in detail as a function of two control parameters: the dc component of the population inversion and the modulation amplitude. Two kinds of optical chaos in two limiting regions reported in a previous paper are extensively studied to clarify their different characteristics from deterministic and stochastic points of view. The competition between their different origins is revealed. Statistical properties of their stochasticity are investigated to clarify their non-Gaussian natures. Comparison with analytical results for a single-mode laser with fluctuations is also made.