Optical anisotropy in GaSe

Optical anisotropy of the layer semiconductor GaSe has been studied by photoluminescence (PL) and Fourier Transform Infrared Spectroscopy (FTIR). The PL spectra are dominated by two closely positioned emission bands resulting from the free exciton and the bound exciton connected direct band edge of GaSe. Photoluminescence and transmission spectra of GaSe crystals have been measured for two cases in which the propagation vector k is perpendicular (k ⟂ c) and parallel to the c‐axis (k // c). Peak position of the PL emission band and the onset of the transmission have been found to be significantly different for these two cases. This observed anisotropy is related to anisotropic band structure and the selection rules for the optical absorption in layered GaSe. FTIR transmission spectrum is in good agreement with PL results. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bis(p‐nitrobenzoxasulfamato) Complexes of Cadmium(II) and Mercury(II) ‐ Synthesis,Spectra, and X‐Ray Crystal Structures

The reaction of sodium benzoxasulfamate (nbs) with cadmium(II) and mercury(II) sulfate in aqueous solution yield the novel complexes [Cd(nbs)₂(H₂O)₄] (1) and [Hg(nbs)₂(H₂O)₃] ( 2 ), respectively. The complexes were characterized by elemental analyses, IR spectroscopy and X‐ray crystallography. Complex 1 is monomeric and has an octahedral arrangement in which the N‐donor nbs ligands occupy the axial positions, while the water oxygen atoms form the equatorial plane. Complex 2 is polymeric and shows a pentagonal bipyramidal arrangement achieved by the bridging of the HgN₂O₃ units through the weak interaction of the O atoms of the nitro group. The nbs ligands also occupy the axial positions of the pentagonal bipyramid, whereas three water and two nitro oxygen atoms constitute the pentagonal plane. The crystal structure packing in both crystals is achieved by the intermolecular hydrogen bonds involving water hydrogen atoms, nitro and sulfonyl oxygen atoms.     

Photoinduced step-growth polymerization of thieno[3,4-b] thiophene derivatives. The substitution effect on the reactivity and electrochemical properties

We herein report photoinduced step-growth polymerization of highly conjugated 2,5-dithiophenyl (thieno[3,4-b] thiophene) (TTs) derivatives possessing 4-cyanophenyl or 4-methoxyphenyl or 3-(4-fluorophenyl) groups substituted at the terminal position. Upon irradiation at 350 nm, the excited state of these molecules forms exciplex with diphenyliodonium hexafluorophosphate (DPI) that undergoes electron transfer reaction forming radical cations. Successive proton release and radical coupling reactions yield corresponding oligothienothiophenes with overall yields varying between 19–74%. Structural and molecular weight characteristics of the oligomers thus formed were investigated by Ultraviolet, fluorescence, NMR (Nuclear Magnetic Resonance) and infrared (IR) spectroscopic methods, and GPC (Gel Permeation Chromatography), respectively. The effect of substitution and dithiophene side groups on the reactivity of the monomer and band gap of the oligomers formed was evaluated by using cyclic voltammetry.     

Spectroscopic ellipsometry study of above-band gap optical constants of layered structured TlGaSe2, TlGaS2 and TlInS2 single crystals

Spectroscopic ellipsometry measurements on TlGaSe₂, TlGaS₂ and TlInS₂ layered crystals were carried out on the layer-plane (0 0 1) surfaces, which are perpendicular to the optic axis c^?, in the 1.2–6.2 eV spectral range at room temperature. The real and imaginary parts of the pseudodielectric function as well as pseudorefractive index and pseudoextinction coefficient were found as a result of analysis of ellipsometric data. The structures of critical points in the above-band gap energy range have been characterized from the second derivative spectra of the pseudodielectric function. The analysis revealed four, five and three interband transition structures with critical point energies 2.75, 3.13, 3.72 and 4.45 eV (TlGaSe₂), 3.03, 3.24, 3.53, 4.20 and 4.83 eV (TlGaS₂), and 3.50, 3.85 and 4.50 eV (TlInS₂). For TlGaSe₂ crystals, the determined critical point energies were assigned tentatively to interband transitions using the available electronic energy band structure.     

3,4‐Bis[(4‐methoxy­benzo­yl)methyl­sulfanyl]thio­phene

A new type of thio­phene derivative having α‐thio­ketone groups at the 3‐ and 4‐positions, viz. the title compound, C₂₂H₂₀O₄S₃, has been prepared and studied by NMR spectroscopy and single‐crystal X‐ray diffraction techniques. The mol­ecule is nearly planar, the dihedral angles between the essentially planar thio­phene and benzene rings being 9.4 (1) and 10.6 (1)°. One of the thio­ketone O atoms is involved in an inter­molecular C—H⋯O hydrogen‐bonding inter­action.     

A Possible Relationship Between Serum Satellite DNA and Cellular Antioxidative Mechanism

The presence of circulating free DNA in the sera of cancer patients has been reported by different authors. Moreover, a hypothetical relationship between the DNA level and different stages of the disease has also been suggested. In this work, the free serum DNA level in various cancer patients was measured and consistent results with the reported data were found. (1,4) To assess the possible mechanism for the release of this fraction and to explain the high levels observed in cancer patients levels of the bivalent intracellularcation, magnesium were determined. Further to relate the process to the antioxidative mechanism of the cell membrane also selenium levels were measured simultaneously. The serum free DNA and the magnesium concentration of the patients before treatment were significally higher and the selenium levels lower than the control group. After appropriate the rapy the magnesium levels were found to decline while the high free DNA and low selenium values still persisted. These findings imply that the membrane stability and permeability is impaired due both to the neoplastic changes and later to the effect of chemotherapeutic agents with the result that intracellular material is released into the circulation.     

Reversible Doping of a Dithienothiophene‐Based Conjugated Microporous Polymer

Dithienothiophene (DTT) based conjugated microporous polymers (CMPs) were synthesized by bulk and electrochemical oxidative polymerizations. Spectroelectrochemical measurements showed that DTT‐CMP can be reversibly oxidized and reduced, accompanied by a significant change of the absorption properties making the material interesting for electrochromic devices. Reversible doping and dedoping of the bulk polymer network was also observed using iodine and ammonia, respectively. Nitrogen gas sorption measurements of the neutral, doped, and dedoped polymer networks indicated the presence of iodide species within the pores, and the conductivity of the networks is highly increased upon doping with iodine. The introduction of the strong electron donor DTT into a conjugated porous network, and the ability for redox switching, make DTT‐CMPs interesting materials for organo(opto)electronic devices and sensors.     

Some metal chelates with Schiff base ligand: synthesis,structure elucidation,thermal behavior,XRD evaluation,antioxidant activity,enzyme inhibition,and molecular docking studies

Molecular Diversity - Schiff bases are well-known compounds for having significant biological properties. In this study, a new Schiff base ligand and its metal complexes were synthesized, and their...