To be or not to be – nematic liquid crystals from shape-persistent V-shaped nematogens with the ‘magic angle’

The tetrahedral bending angle in V-shaped nematogens was claimed to be the optimum for finding a biaxial nematic liquid crystal phase. The benzo[1,2-b:4,3-b’]dithiophene core, recently successfully applied as a tetrahedral bending unit in mesogens with lateral flexible chains, is here embedded in a scaffold with only terminal chains, which conventionally promotes the formation of nematic phases at low temperature. A series of new mesogens has been successfully prepared, realising hockey-stick, hockey-stick dimer and V-shaped molecular topologies. Only the hockey-stick mesogens assemble in uniaxial nematic phases over a broad temperature range. Single crystal structure analysis of a hockey-stick and V-shaped compound reveal remarkable similarities with the benzodithiophene core wrapped by aliphatic chains. A model explaining the absence of nematic mesophases in the family of V-shaped, shape-persistent mesogens with terminal aliphatic chains is presented and results in the proposal of a new design for biaxial nematogens.     

Analytical performance of an r.f. capacitively coupled plasma for atomic emission with tip-ring electrode geometry

A low to medium power radiofrequency capacitively coupled plasma is characterized as spectral source for atomic emission. The signal to background ratio and the limits of detection were determined for 19 elements as a function of the plasma torch geometry and the observation point.     

Base-Assisted Imidization: A Synthetic Method for the Introduction of Bulky Imide Substituents to Control Packing and Optical Properties of Naphthalene and Perylene Imides

We report the direct imidization of naphthalene and perylene dicarboxylic anhydrides/esters with bulky ortho,ortho-diaryl- and ortho,ortho-dialkynylaniline derivatives. This imidization method uses n-butyllithium as a strong base to increase the reactivity of bulky amine derivatives, proceeds under mild reaction conditions, requires only stoichiometric amounts of reactants and gives straightforward access to new sterically crowded rylene dicarboximides. Mechanistic investigations suggest an isoimide as intermediary product, which was converted to the corresponding imide upon addition of an aqueous base. Single-crystal X-ray diffraction analyses reveal dimeric packing motifs for monoimides, while two-side shielded bisimides crystallize in isolated molecules without close π–π-interactions. Spectroscopic investigations disclose the influence of the bulky substituents on the optical properties in the solid state.     

In vivo imaging of the human brain at 1.5 T with 0.6-mm isotropic resolution

We present high-resolution in vivo anatomical scans with 3D whole-brain coverage and an isotropic resolution of 0.6 mm, obtained at a clinical field of 1.5 T. The data are acquired in 10 independent scans over two sessions using a 3D magnetization-prepared, gradient echo sequence, modified to output phase images in addition to magnitude images. The independent scans are coregistered to correct for head motion, prior to performing complex averaging. The resolution of the final, averaged image, is found to be equal to the nominal one.     

The analysis of conductive solid samples by r.f. capacitively coupled plasma at atmospheric pressure

A radiofrequency capacitively coupled plasma (rf CCP) with tip-ring electrode geometry has been used for the analysis of Al, Co, Cr, Cu, Mn, Mo, Ni, and V in low and medium alloyed steel. The sample is used as one of the electrodes of the plasma torch. The influence of plasma power, argon flow rate and distance between the electrodes on the analytical signals has been studied. The limits of detection are in the range of 0.001 to 0.048%. The dynamic range is three orders of magnitude.     

Upconversion luminescence of Er3+/Yb3+ co-doped nanolangasite synthesized by a modified Pechini route

Nanopowders of langasite (La₃Ga₅SiO₁₄) doped with 1 at.% Er³⁺ and 3 at.% Yb³⁺ were synthesized for the first time by a modified Pechini route and annealed in air at 700, 750, 800, 900, and 1,000?°C. The langasite powders were characterized by XRD, FTIR and luminescence techniques. Crystallization began at 750?°C and pure langasite phase was obtained for the samples annealed at 800 and 900?°C. Traces of LaGaO₃ and Ga₂O₃ were observed in the sample annealed at 1,000?°C. Bright green and red luminescence was observed for pumping at 973?nm whose intensity increased with annealing temperature due to the removal of the adsorbed impurities and the improvement of crystallinity.     

Characteristic temperatures and electron number densities in an R.F. capacitively coupled plasma

The excitation temperatures of Ar and Fe, the ionization temperatures of Ar and Ca and the electron number densities have been determined for a radiofrequency capacitively coupled plasma in the tip-ring electrode geometry. The temperatures and the electron number densities possess their maximum value close to the electrodes.     

Study of the 2-Benzimidazolylaminomethylphosphonic Acid Derivatives by Mass Spectroscopy

Abstract

The present paper reports the mass spectra of some compounds of 2-alkylenbenzimidazolylaminomethylphosphonates with the general formula: