New nonlinear optical polyamides: Influence of binding mode of side-chains and rigidity of main-chains on temporal stability

New nonlinear optical rigid polyamides were synthesized and the influence of the binding mode between nonlinear optical chromophores and oxybutyl spacers, as well as of the rigidity of the main-chain on the second-order nonlinearity were investigated. The polyamides with side-on binding mode exhibit higher temporal stability of the polar order than analogous polyamide with end-on binding mode. By decreasing the rigidity of the main-chain of side-on polyamides, polyamide with 4,4’-methylenedianiline reveals enhanced solubility and processability, still keeping a high temporal stability compared to the relatively rigid polyamide with 1,4-phenylenediamine.     

A review: a comparison of different adsorbents for removal of Cr (VI), Cd (II) and Ni (II)

A review of the studies dealing with the removal of chromium, cadmium, and nickel ions with different adsorbents published in the literature between 2014 and 2018 is given in tabular form, along with the adsorption conditions, adsorption isotherm, and kinetic models applied by the authors to model the experimental data and adsorption capacities. The review focuses on the efficiency of ion removal.     

Switching mechanism in polar columnar mesophases made of bent-core molecules.

The behaviour of polar, broken-layer-type columnar phases made of bent molecules (B(1Rev) and B(1RevTilted)) was studied under an applied electric field. There are two competing mechanisms of ferroelectric switching in the polar B(1RevTilted) columnar phase: collective rotation around the long molecular axis and collective rotation around the tilt cone. The proposed model shows that the main factor discriminating the type of switching is the width of the column cross-section.     

A phenomenological model of antiferroelectric liquid crystals

Abstract

We present the analysis of static properties of a simple phenomenological model of antiferroelectric liquid crystals, capable of explaining some different sequences of phase transitions found experimentally. Stability analysis shows the existence of three simply modulated phases. Results are summed up in phase diagrams with dependence on the parameters of the model. The existence of doubly modulated incommensurate phases is predicted in parts of the phase diagrams.     

Synthesis and structure of bis- and tris-ferrocene containing N-methylimide foldamers

The synthesis and conformational analysis of dimer Fc–CO–NMe–CO–Fc (5) and trimer Fc–CO–NMe–CO–Fn–CO–NMe–CO–Fc (6) have been described. It has been shown by means of spectroscopic studies, X-ray crystallography, and molecular modeling, that these molecules are dominated by cis–cis conformation. Furthermore, we recognized for the first time, that such type of organometallics possess elements of chiral helicity. Their crystal lattices are characterized by π–π and CH–π intermolecular interactions (5) and by CH?OC intermolecular hydrogen bonds (6). We believe that foldamers 5/6 are stabilized by the special type of aromatic π–π interactions between the closer cyclopentadienyl rings of the juxtaposed ferrocene units.     

A microfluidic diffusion chamber for reversible environmental changes around flaccid lipid vesicles

The reversible environmental changes around flaccid lipid vesicles represent a considerable experimental challenge, particularly because of remarkable softness of flaccid membranes, which can warp irreversibly under the slightest hydrodynamic flow. As a result, we have developed a microfluidic device for the controlled analysis of individual flaccid, giant lipid vesicles in a changing chemical environment. The setup combines the advantages of a flow-free microfluidic diffusion chamber and optical tweezers, which are used to load the sample vesicles into the chamber. After a vesicle is loaded into the diffusion chamber, its chemical environment is controllably and reversibly changed solely by means of diffusion. The chamber is designed as a 250 micrometres-long and 100 micrometres-wide dead-end microchannel, which extends from a T-junction of the main microchannels. Measurements of the flow-velocity profile in the chamber show that the flow rate decreases exponentially and scales linearly with the flow rate in the main channel. The characteristic length of the exponential decrease is 15 (1 ± 0.13) micrometres, meaning that a large part of the diffusion chamber is effectively flow-free. The diffusion properties are assessed by monitoring the diffusion of a dye into the chamber. It was found that a simple 1D diffusion model fits well to the experimental data. The time needed for the exchange of solutes in the chamber is of the order of minutes, depending on the solute's molecular weight. Here, we demonstrate how the diffusion chamber can be used for reversible environmental changes around flaccid, giant lipid vesicles and membrane tethers (nanotubes).     

Electron–phonon coupling and vibrational modes contributing to linear electro‐optic effect of the efficient NLO chromophore 4‐(N,N‐dimethylamino)‐N‐methyl‐4′‐toluene sulfonate (DAST) from their vibrational spectra

The optimized geometry and structural features of the most prospective electro‐optic crystal 4‐(N,N‐dimethylamino)‐N‐methyl‐4′‐toluene sulfonate (DAST), and the vibrational spectral investigations have been comprehensively described with the near infrared Fourier transform (NIR FT) Raman and Fourier transform infrared (FT‐IR) spectra supported by the density functional theoretical (DFT) computations to elucidate the contribution of vibrational modes to the linear electro‐optic (LEO) effect. Mulliken population analysis and natural bond orbital (NBO) analysis have also been carried out to analyze the effects of intramolecular charge transfer (ICT), intramolecular hydrogen bonding and hyperconjugative interactions on the geometries. The influence of CT interaction between the phenyl ring and the dimethylamino group of the nonlinear optical (NLO) chromophore on the endocyclic and exocyclic angles, and the electronic effects such as hyperconjugation and back‐donation on the methyl hydrogen atoms have been examined. The concurrent intense activation of Raman and IR activities of the effective conjugation vibrational coordinate, which significantly contributes to the LEO effect resulting from the strong electron–phonon (e/ph) coupling, has been analyzed in detail. The effects of frontier orbitals, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), transition of electron density (ED) transfer and the influence of planarity in the stilbazolium ring on the first hyperpolarizability are also discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

A General Synthetic Route to High-Quality Perovskite Oxide Nanoparticles and Their Enhanced Solar Photocatalytic Activity

The main limitations of current methods for synthesizing perovskite oxide (ABO₃) nanoparticles (NPs), e.g., the high reagent costs and sophisticated equipment, the long time and high-temperature processing, or multiple post-processing and thermal treatment steps, hamper their full study and potential application. Here, we use a facile low temperature (50 °C) chemical bath synthesis and only one annealing step to successfully produce high phase purity and crystalline quality nano-shaped rare-earth-based REMO₃ NPs (RE=La, Nd, Sm, Gd; M=Fe, Mn, Al). We also show the versatility of this approach by fabricating La_0.7Sr_0.3MnO₃ solid solution and non-RE-based BiFeO₃ perovskite. To assess the potential of the as-prepared REFeO₃ and REMnO₃ NPs, they are used for photocatalytic degradation of the norfloxacin antibiotic and show high efficiency. We believe this easy, robust, versatile, and general route for synthesizing ABO₃-based NPs can be further explored in the vast perovskite family and beyond.