Production and Neutron Irradiation Tests on a New Epoxy/Molybdenum Composite

Molybdenum powder was added in an epoxy matrix to increase the neutron-shielding capacity of pure epoxy. FLUKA and GEANT4 Monte Carlo programs were used to design new neutron-shielding material. After finding the epoxy/Mo ratio for the best shielding capacity, neutron equivalent dose rate measurements were performed. Results were compared to commonly used neutron-shielding materials such as paraffin, steel, concrete, and B₄C. The produced new sample has a high neutron shielding capacity and it can be used for neutron protection purposes.     

Crystal Structure and Conformational Analysis of 4-[(<Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Dimethylamino)Benzylidene]-2-Phenyloxazole-5-One

Abstract  

Molecular and crystal structure of 4-[(p-N,N-dimethylamino)benzylidene]-2-phenyloxazol-5-one, C₁₈H₁₆N₂O₂, have been determined by single crystal X-ray diffraction study. The title compound is monoclinic, with a = 12.1704(23) ?, b = 3.9810(5) ?, c = 30.9603(56) ?, β = 101.176(15)°, Z = 4, D _x = 1.32 g/cm³, μ(Mo Kα) = 0.087 mm⁻¹, and space group is P12₁/c1. The structure was solved by direct methods and refined to a final R = 0.047 for 3166 reflections with I > 2σ(I). The crystal structure is stabilized by C–H⋯O and C–H⋯N type intra-molecular, C–H⋯O type inter-molecular interactions. To enlighten the flexibility and the geometric isomerism (E or Z) of the title compound, the selected torsion angle is varied from −180 to 180° in every 10° separately and molecular energy profile is calculated and analyzed.     

Supramolecular Architecture in the 1:1 Co-Crystallization of 6,7-Dimethoxy-2-methyl-4-phenylisoquinolinium Cation with Perchlorate Anion

Abstract  X-ray crystallographic analysis of the title organic ion–pair complex, C₁₈H₁₈NO₂ ⁺ · ClO₄ ⁻, reveals that 6,7-dimethoxy-2-methyl-4-phenylisoquinolinium cation is co-crystallized with perchlorate counter-anions in 1:1 ratio. The complex crystallizes in space group P 2 ₁ /n, with a = 8.0226(7) ?, b = 12.2552(7) ?, c = 17.9734(16) ?, β = 93.908(7) °, Z = 4, D _x  = 1.431 g/cm³. Aromaticity of isoquinolinium fragment is considerably deformed by the existence of C–H···O type weak H-bonds, leading to chains of topology C ₃ ³(12)[R ₁²(4)] running along b-axis of the unit cell and pseudo-cyclic centrosymmetric R ₄⁴(24)[2R ₁²(4)] synthons. The weak H-bonds serve to stabilize both the extended structure and molecular geometry of the title complex, in particular the disordered perchlorate anion whose components adopt a distorted tetrahedron. Index Abstract  Molecular and the extended structure of 6,7-dimethoxy-2-methyl-4-phenylisoquinolinium perchlorate, C₁₈H₁₈NO₂ ⁺ · ClO₄ ⁻, were determined by single crystal X-ray diffraction study.     

Supramolecular architecture of phenylcarbamoylated acetone oxime 1,1-diisopropyl-3-phenylurea] complex

Carbamoylated oximes 1 form 1:1 molecular complexes 4 with N,N-dialkyl-N′-phenylurea when stirred in THF or ether at room temperature for short time in good yields. The molecular complexes 4a–e were isolated and characterized by analytical and spectral means. X-ray crystallographic analysis for complex 4a was performed. In this paper, we report the use of complex 4a and its moieties as building blocks to form non-interacting polymeric zigzag chains by inter- and intramolecular hydrogen bonds along b-axis, and details of supramolecular architecture of 4a. There is a intramolecular H–H interaction between hydrogen of urea NH and neighboring hydrogen of diisopropyl's CH linked to the other urea nitrogen. In addition, to obtain the most favorable orientation of the moieties of the title complex, PM3 semi-empirical quantum mechanical calculations were performed and then results from X-ray crystallography and computational modeling were compared.

Exciton Migration and Surface Trapping for a Photonic Crystal Displaying Charge‐Recombination Fluorescence

A compact donor–acceptor molecular dyad has been synthesized by attaching an N,N‐dimethylamino fragment to a naphthalic anhydride residue. The dyad shows fluorescence from an intramolecular charge‐transfer state (i.e., charge‐recombination fluorescence) in solution, with the photo‐physical properties being strongly dependent on the solvent polarity. Similar emission is seen for single crystals of the target compound, the molecules being aligned head‐to‐head, although time‐resolved emission profiles display dual‐exponential kinetics. A second polymorph with the head‐to‐tail alignment also gives rise to two lifetimes that differ somewhat from those of the first structure, which are assigned to bulk and surface‐bound molecules. Growing the crystal in the presence of Rhodamine B localizes the dye around the surface. Excitation of the crystal is followed by sub‐ps exciton migration along the aligned stacks, with occasional crossing to adjacent stacks and trapping at the surface. Rhodamine B present at very low levels acts as the acceptor for excitons entering the surface layer. Crystals embedded in a polyester resin form an artificial light‐harvesting antenna able to sensitize an amorphous silicon solar cell.     

Energy-momentum localization in Marder space-time

Considering the Einstein, Møller, Bergmann-Thomson, Landau-Lifshitz (LL), Papapetrou, Qadir-Sharif and Weinberg’s definitions in general relativity, we find the momentum four-vector of the closed Universe based on Marder space-time. The momentum four-vector (due to matter plus field) is found to be zero. These results support the viewpoints of Banerjee-Sen, Xulu and Aydo?du-Salt?. Another point is that our study agrees with the previous works of Cooperstock-Israelit, Rosen, Johri et al.     

Photodegradation of C‐PCPDTBT and Si‐PCPDTBT: Influence of the Bridging Atom on the Stability of a Low‐Band‐Gap Polymer for Solar Cell Application

The kinetics of photodegradation and the reactivity of different sites of the low‐band‐gap polymers poly[2,6‐(4,4‐bis‐(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene)‐alt‐4,7‐(2,1,3‐benzothiadiazole)] (C‐PCPDTBT) and poly[2,6‐(4,4‐bis‐(2‐ethylhexyl)dithieno[3,2‐b:2′,3′‐d]silole)‐alt‐4,7‐(2,1,3‐benzothiadiazole)] (Si‐PCPDTBT) are investigated as thin films and are compared to those of poly(3‐hexylthiophene) (P3HT). The decay kinetics are monitored with UV/Vis spectroscopy and the reactivity and product evolution are investigated with X‐ray photoelectron spectroscopy (XPS). Both polymers exhibit higher stability than P3HT. The bridging atom in the cyclopentadithiophene (CPDT) subunit has a significant influence on the stability. Varying oxidation rates for the different elements were observed. In the case of Si‐PCPDTBT, the silicon atom is oxidized primarily, whereas the photooxidation rates of the other elements are reduced relative to C‐PCPDTBT. Additionally, XPS experiments with varying excitation energies reveal a significant reaction gradient within a few nanometers of the surface of degraded thin films of C‐PCPDTBT.