New optical limiting polymeric materials with different π-electron conjugation bridge structures: Synthesis and characterization

In this communication we describe the design and synthesis of five new conjugated polymers (P1–P5) with various π-electron conjugation bridges. Their structures were established by FTIR, ¹H NMR spectroscopy, elemental analysis. The molecular weights of the polymers were estimated by gel permeation chromatographic technique. Further, their electrochemical, linear and nonlinear optical properties were investigated. The electrochemical band gaps of P1–P5 were found to be 1.72–2.35 eV. Their third-order nonlinear optical activities were studied by open aperture Z-scan technique, using a Q-switched, frequency doubled Nd:YAG laser producing 7 nano second laser pulses at 532 nm. Z-scan results reveal that the polymers exhibit self-defocusing nonlinearity and their operating mechanism involves reverse saturable absorption. The polymers showed strong optical limiting behavior due to effective two-photon absorption (2PA) with 2PA coefficients of the order of 10^?11 m/W, which is comparable to that of good optical limiting materials in the literature.     

Josephson oscillation of a superfluid Fermi gas

Using the complete numerical solution of a time-dependent three-dimensional mean-field model we study the Josephson oscillation of a superfluid Fermi gas (SFG) at zero temperature formed in a combined axially-symmetric harmonic plus one-dimensional periodic optical-lattice (OL) potentials after displacing the harmonic trap along the axial OL axis. We study the dependence of Josephson frequency on the strength of the OL potential. The Josephson frequency decreases with increasing strength as found in the experiment of Cataliotti et al. [Science 293, 843 (2001)] for a Bose-Einstein condensate and of the experiment of Pezzè et al. [Phys. Rev. Lett. 93, 120401 (2004)] for an ideal Fermi gas. We demonstrate a breakdown of Josephson oscillation in the SFG for a large displacement of the harmonic trap. These features of Josephson oscillation of a SFG can be tested experimentally.     

Amperometric determination of 2-benzothiazole sulphenamide accelerators

A simple method for the amperometric estimation of N-cyclohexyl-2-benzothiazole sulphenamide, N-dicyclohexyl-2-benzothiazole sulphenamide, 2-(morpholinothio)benzothiazole and N-tert.-butyl-2-benzothiazole sulphenamide is reported. The results are obtained within 5 min and are correct within +/- 2.0%.     

Molecular deformation mechanisms of isotactic polypropylene in α‐ and β‐crystal forms by FTIR spectroscopy

The orientation behavior of isotactic polypropylene (iPP) in α‐ and β‐crystal form was investigated by rheo‐optical Fourier transformed infrared (FTIR) spectroscopy. This method enabled quantification of the degree of orientation as a feature of structural changes during uniaxial elongation in not only the crystalline phase but also the amorphous one. Molecular orientation mechanisms can be successfully derived from experimental results. Generally, three mechanisms were detected for iPP: (1) interlamellar separation in the amorphous phase, (2) interlamellar slip and lamellar twisting at small elongations, and (3) intralamellar slip at high elongations. The third mechanism was favored by α‐PP, whereas β‐PP favored the second mechanism, which, in fact, was responsible for the different mechanical properties of both materials at the macroscopic level. On the other hand, crystallization conditions may have significantly affected the amorphous orientation. Nevertheless, for both iPP types the chains in the amorphous phase always oriented less than did those in the crystalline phase. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4478–4488, 2004     

Diethyl 1-(p-fluoro­phenyl)-5-oxo-3-(2-thienyl)­pyrrolidine-2,2-di­carboxyl­ate

In the title compound, C₂₀H₂₀FNO₅S, the pyrrolidine ring adopts an envelope conformation. The fluoro­phenyl and thio­phene rings are individually planar. The molecular and crystal structures are stabilized by intra- and intermolecular C—H⋯O interactions.     

Oxidation reactions of 1,3-diphenylpropane-1,3-dione

The free radical scavenging properties and possible antioxidant activity of 1,3-diphenylpropane-1,3-dione (1) are reported. Pulse radiolysis technique was employed to study the one-electron oxidation of 1 with various radicals viz. CCl₃O₂ ^•, N₃ ^• and^•OH in homogeneous aqueous solution. All these radicals reacted with 1 under ambient conditions at almost diffusion controlled rates producing transient species with an absorption maximum around 420 nm that decayed at first order rates. The transient absorption peak was shifted in the case of CCl₃OO^• radical reaction with 1 due to change in the polarity of the medium. Formation of a stable product with a broad absorption band starting from 400 nm and cut off at 230 nm was observed in the oxidation of 1 with^•OH and^•N₃ radicals. In a biological system also, 1 showed significant inhibitory activity against Fe²⁺-mediatedlipidperoxidation. Based on these observations, a suitable mechanism for the oxidation of 1 has been proposed.     

Allosteric effect of the first lead ion on stepwise extraction of the second lead ion with p-t-butylcalix[5]arene pentacarboxylic acid derivative

A calix[5]arene-based solvent extraction reagent displaying very high selectivity for lead has been prepared, one molecule of which extracts two lead ions in a stepwise manner. The first Pb²⁺ ion is bound to five phenoxy oxygen atoms inside the calixarene cavity due to which the ligand undergoes conformational freezing in stable cone conformer. This causes positive allosteric effect for co-extraction of the second lead ion due to the aggregation of functional groups.     

Diabatization of the reactive F + H<Subscript>2</Subscript> system employing rigorous Berry phases

In this article are presented the first ever derived single-valued diabatic potentials for the reactive H₂ +  F system based on a rigorous study of the conical intersection (ci) and Born-Oppenheimer non-adiabatic coupling terms (BO NACTs). This study revealed the existence of a Jahn-Teller (1, 2) ci located at a point on the collinear axis and a Renner-Teller (2, 3) ci along this axis. The diabatic potentials were calculated employing the rigorous adiabatic-to-diabatic transformation (ADT) angles (also known as mixing angles) which possess integer Berry phases along any closed contour at the region of interest in configuration space. The ADT angles were calculated employing BO NACTs and line integrals.     

Axial instability of double-nanobeam-systems

This Letter considers the axial instability of double-nanobeam-systems. Eringen's nonlocal elasticity is utilized for modelling the double-nanobeam-systems. The nonlocal theory accounts for the small-scale effects arising at the nanoscale. The small-scale effects substantially influence the instability (or buckling) of double-nanobeam-systems. Results reveal that the small-scale effects are higher with increasing values of nonlocal parameter for the case of in-phase (synchronous) buckling modes than the out-of-phase (asynchronous) buckling modes. The increase of the stiffness of the coupling elastic medium in double-nanobeam-system reduces the small-scale effects during the out-of-phase (asynchronous) buckling modes. Analysis of the scale effects in higher buckling loads of double-nanobeam-system with synchronous and asynchronous modes is also discussed in this Letter. The theoretical development presented herein may serve as a reference for nonlocal theories as applied to the instability analysis of complex-nanobeam-system such as complex carbon nanotube system.