Dielectric and visco-elastic properties of laterally fluorinated liquid crystal single compounds and their mixture

The physical properties of three laterally fluorinated liquid crystalline compounds with negative dielectric anisotropy have been studied from static dielectric permittivity, optical birefringence, bend elastic constant, relaxation time and rotational viscosity measurements. Such negative dielectric anisotropy materials find use as components of mixtures for application in vertically aligned mode liquid crystal displays. Moreover, the physical properties of one phenyl cyclohexane compound with positive dielectric anisotropy have also been studied. A five-component mixture comprising these four mesogens and a non-mesogenic component has been formulated and its physical properties have been thoroughly investigated. An attempt has been made to strike a balance between the optical birefringence of the mixture to adjust the cell gap and the dielectric anisotropy and threshold voltage (V_th ) to ensure low driving voltages. The pretilt angle effect on the threshold voltage and the relaxation time has also been studied. At T?=?20°C, the response time decreases to 22% and 41% for the mixture for 2° and 5° pretilt as compared to zero pretilt. On the other hand, at the same temperature the V_th values are decreased by 5% and 9%, respectively.     

Mechanistic studies on the intramolecular electron transfer in an adduct species of the oxo-centred trinuclear iron(III) cation and <Emphasis Type="SmallCaps">l</Emphasis>-ascorbic acid in aqueous solution

The kinetics of the intra-molecular electron transfer of an adduct of l-ascorbic acid and the [Fe₃^IIIO(CH₃COO)₆(H₂O)₃]⁺ cation in aqueous acetate buffer was studied spectrophotometrically, over the ranges 2.55 ≤ pH ≤ 3.74, 20.0 ≤ θ ≤ 35.0 °C, at an ionic strength of 0.50 and 1.0 mol dm⁻³ (NaClO₄). The reaction of l-ascorbic acid and the complex cation involves the rapid formation of an adduct species followed by a slower reduction in the iron centres through consecutive one-electron transfer processes. The final product of the reaction is aqueous iron(II) in acetate buffer. The proposed mechanism involves the triaqua and diaqua-hydroxo species of the complex cation, both of which form adducts with l-ascorbic acid. At 25 °C, the equilibrium constant for the adduct formation was found to be 86 ± 15 and 5.8 ± 0.2 dm³ mol⁻¹ for the triaqua and diaqua-hydroxo species, respectively. The kinetic parameters derived from the rate expression have been found to be: k ₀ = (1.12 ± 0.02) × 10⁻² s⁻¹ for the combined spontaneous decomposition and k ₁ = (4.47 ± 0.06) × 10⁻² s⁻¹ (ΔH ₁^‡ = 51.0 ± 2.3 kJ mol⁻¹, ΔS ₁^‡ = −100 ± 8 J K⁻¹ mol⁻¹), k ₂ = (4.79 ± 0.38) × 10⁻¹ s⁻¹ (ΔH ₂^‡ = 76.5 ± 0.8 kJ mol⁻¹, ΔS ₂^‡ = 6 ± 3 J K⁻¹ mol⁻¹) for the triaqua and diaqua-hydoxo species, respectively.     

Controlled porosity monolithic material as permselective ion exchange membranes

Ion exchange membranes (IEMs) are used in a variety of analytical devices, including suppressors, eluent generators and other components used in ion chromatography. Such membranes are flexible and undergo substantial dimensional changes on hydration. Presently the push to miniaturization continues; a resurgent interest in open tubular ion chromatography requires microscale adaptation of these components. Incorporating IEMs in microscale devices is difficult. Although both macroporous and microporous ion exchange materials have been made for use as chromatographic packing, ion exchange material used as membranes are porous only on a molecular scale. Because such pores have vicinal ion exchange sites, ions of the same charge sign as those of the fixed sites are excluded from the IEMs. Monolithic polymers, including ion exchangers derived therefrom, are presently extensively used. When used in a separation column, such a monolithic structure contains an extensively connected porous network. We show here that by controlling the amount of porogen added during the synthesis of monolithic polymers derived from ethylene dimethacrylate – glycidyl methacrylate, which are converted to an anion exchanger by treatment with trimethylamine, it is possible to obtain rigid ion exchange polymers that behave like IEMs and allow only one charge type of ions to pass through, i.e., are permselective. We demonstrate successful open tubular cation chromatography suppressor performance.     

Low-threshold operation of a 355-nm pumped nanosecond β-BaB2O4 optical parametric oscillator

We report the low-threshold operation of a nanosecond β-BaB₂O₄ optical parametric oscillator (OPO) pumped by the third harmonic of a Q-switched Nd:YAG laser. Using cylindrical focusing of the pump beam, a threshold pulse energy of 0.5 mJ is obtained at the signal wavelength of 560 nm, which is about sixteen times lower than that of a spherical focusing configuration. The importance of diffraction loss in the design of tightly focused OPOs is discussed in terms of a simple extension of the conventional OPO model.     

Identifying neutrino mass hierarchy at extremely small theta13 through earth matter effects in a supernova signal

Collective neutrino flavor transformations deep inside a supernova are sensitive to the neutrino mass hierarchy even at extremely small values of theta_(13). Exploiting this effect, we show that comparison of the antineutrino signals from a galactic supernova in two megaton class water Cherenkov detectors, one of which is shadowed by Earth, will enable us to distinguish between the hierarchies if sin(2)theta_(13) < or approximately 10(-5), where long baseline neutrino experiments would be ineffectual.     

Disentangling effects of nuclear structure in heavy element formation

Forming the same heavy compound nucleus with different isotopes of the projectile and target elements allows nuclear structure effects in the entrance channel (resulting in static deformation) and in the dinuclear system to be disentangled. Using three isotopes of Ti and W, forming 232Cm, with measurement spanning the capture barrier energies, alignment of the heavy prolate deformed nucleus is shown to be the main reason for the broadening of the mass distribution of the quasifission fragments as the beam energy is reduced. The complex, consistently evolving mass-angle correlations that are observed carry more information than the integrated mass or angular distributions, and should severely test models of quasifission.     

Photophysical and laser characteristics of pyrromethene 567 dye: Experimental and theoretical studies

Narrow-band laser performance of alcohol solutions of pyrromethene 567 (PM567) and rhodamine 6G (RH6G) dye was investigated using a home-made GIG-configured dye laser, excited by the second-harmonic radiation (at 532 nm) of a pulsed Nd:YAG laser. Higher laser efficiency was observed with PM567 dye (∼23% peak) in comparison to the commonly used RH6G dye (16.5%), in spite of much lower fluorescence quantum efficiency of the PM567 (0.83) vis-à-vis RH6G (0.98) dye solutions in ethanol. First principle-based electronic structure calculations were performed on PM567 dye in the ground (S ₀) and excited states (S ₁) using density functional theory to elucidate the structure and photophysical properties of the dye.     

Ligand-Mediated Revival of Degraded α-CsPbI3 to Stable Highly Luminescent Perovskite

Although α-CsPbI₃ is regarded as an attractive optical luminophore, it is readily degraded to the optically inactive δ-phase under ambient conditions. Here, we present a simple approach to revive degraded (“optically sick”) α-CsPbI₃ through “medication” with thiol-containing ligands. The effect of different types of thiols is systematically studied through optical spectroscopy. The structural reconstruction of degraded α-CsPbI₃ nanocrystals to cubic crystals in the presence of thiol-containing ligands is visualized through high-resolution transmission electron microscopy and supported by X-ray diffraction analysis. We found that 1-dodecanethiol (DSH) effectively revives degraded CsPbI₃ and results in high immunity towards moisture and oxygen, hitherto unreported. DSH facilitates the passivation of surface defects and etching of degraded Cs₄PbI₆ phase, thus reverting them back to the cubic CsPbI₃ phase, leading to enhanced PL and environmental stability.     

Chemodosimetric Mechanistic Insight through Trapping Intermediate for Selective Detection of Picric Acid in Aqueous Medium by a Dinuclear CdII Complex

A fluorescent dinuclear cadmium(II) based discrete metal complex of composition [Cd^II₂L(μ-Cl)Cl₂]( 1 ) is used {HL=2,6-bis[2-(methylamino)ethyliminomethyl]-4-Ethylphenol} for the specific recognition of 2,4,6-trinitrophenol (picric acid; PA) via fluorescence quenching phenomenon among various nitroaromatic compounds through a chemodosimetric approach. It has been established that 1 is a chemodosimeter in pure water. We have successfully been able to isolate three compounds: chemodosimeter 1 ; an intermediate complex 2 of composition [Cd^II(LH₂)Cl₂](Picrate) and final association complex 3 of composition [NH₃(CH₂CH₂)NH₂CH₃](Picrate)₂. Compounds have been characterised by CHN elemental analyses, single crystal X-ray crystallography, PXRD, NMR and FTIR. Selective interaction of 1 with PA was evaluated by fluorescence, UV-Vis and life time measurements. Fluorescence quenching of 1 occurs definitely due to the formation of compound 3 via intermediate 2 involving partial decomplexation, hydrolysis and proton transfer phenomena in solution during the course of sensing. The quenching constant (K_sv), association constant (K_a) and detection limit (LOD) of the complex 1 for picric acid are ∼1.55×10⁵ M⁻¹, ∼1.8×10¹⁰ M⁻² and ∼0.47 μM (0.108 ppm), respectively. Mechanism of sensing is proposed and the very rare case of isolation and characterization of intermediate in picric acid sensing is discussed.