Phase matching second harmonic generation at 0.8716 μm in a Na2SeO4·H2SeO3·H2O crystal

Na₂SeO₄·H₂SeO₃H₂O are transparent orthorhombic (class group mm2) crystals which exhibit interesting second order nonlinear optical properties in the blue region of the visible spectrum. We demonstrate here the efficient generation at λ_ω=0.8716 μm of the second harmonic in a peculiar crystal configuration where type I phase matching occurs.     

Synthesis of ferrocene paracyclophanes

Paracyclophanes containing one or two ferrocene units can be efficiently synthesized directly from 1,1′-di(hydroxymethyl)ferrocene and aromatic dithiols. In the reaction with di(4,4′-dimercaptomethylphenyl)methane the mononuclear paracyclophane was formed, while with the dithiophenols di(4,4′-dimercaptophenyl)methane and di(4,4′-dimercaptophenyl)ether, cyclophanes bearing two ferrocene units were obtained. For comparison three open-chain analogues were also prepared.     

Arylidene imidazothiazoles. Synthesis,structure and benzodiazepine receptor binding

A series of arylidene imidazo[2,1-b]thiazoles was synthesized, in order to investigate the influence of different spatial arrangements of the arylidene substituent towards the bicyclic structure of imidazo[2,1-b]-thiazole on benzodiazepine receptor affinity. 1,2- And 2,3-cyclized derivatives of mono- and di-substituted Z-5-arylidene-2-thiohydantoins were investigated. As an example of E isomers E-5-benzylidene-2,3-dihydroimidazo[2,1-b]thiazol-6(5H)-one was obtained. The spatial arrangement of the arylidene sub stituent toward the bicyclic structure as well as the character of isomers had little influence on the benzo diazepine receptor affinity of the compounds. It seems that the greatest influence on biological activity has the nature and the number of substituents on the phenyl ring. All investigated imidazo[2,1-b]thiazoles were less active than previously described arylidene imidazo[2,1-b]thiazepinones.     

An Improved Synthesis of L-Homohistidine

Bloemhoff - Kerling's method of L-homohistidine synthesis was modified by employing formamidine acetate in liquid ammonia for imidazole ring formation. The improved procedure significantly shortened the synthetic pathway and resulted in enhanced yield.     

Copper- or manganese-doped ZnS quantum dots as fluorescent probes for detecting folic acid in aqueous media

3-Mercaptopropionic acid-capped core/shell ZnS:Cu/ZnS and ZnS:Mn/ZnS doped quantum dots (QDs) prepared through hydrothermal methods exhibit high photoluminescence intensity as well as good photostability. These water-dispersible nanoparticles exhibit high fluorescence sensitivity to folic acid due to the high affinity of the carboxylate groups and nitrogen atoms of folic acid towards the Zn surface atoms of the doped dots. Quenching of the fluorescence intensity of the QDs allows the detection of folic acid concentrations as low as 11 μM, thus affording a very sensitive system for the sensing of this biologically active molecule in aqueous solution. The possible quenching mechanism is discussed.     

Excitation-wavelength Dependent Fluorescence of Ethyl 5-(4-aminophenyl)-3-amino-2,4-dicyanobenzoate

The excitation wavelength dependence of the steady-state and time-resolved emission spectra of ethyl 5-(4-aminophenyl)-3-amino-2,4-dicyanobenzoate (EAADCy) in tetrahydrofuran (THF) at room temperature has been examined. It is found that the ratio of the fluorescence intensity of the long-wavelength and short-wavelength fluorescence bands strongly depends on the excitation wavelength, whereas the wavelengths of the fluorescence excitation and fluorescence bands maxima are independent on the observation/excitation wavelengths. The dynamic Stokes shift of fluorophore in locally excited (LE) and intramolecular charge transfer (ICT) states has been studied with a time resolution about 30 ps. The difference between Stokes shift in the LE and ICT states was attributed to the solvent response to the large photoinduced dipole moment of EAADCy in the fluorescent charge transfer state. On this base we can state that, the relaxation of the polar solvent molecules around the fluorophore was observed.     

The circumference of the square of a connected graph

The celebrated result of Fleischner states that the square of every 2-connected graph is Hamiltonian. We investigate what happens if the graph is just connected. For every n ≥ 3, we determine the smallest length c(n) of a longest cycle in the square of a connected graph of order n and show that c(n) is a logarithmic function in n. Furthermore, for every c ≥ 3, we characterize the connected graphs of largest order whose square contains no cycle of length at least c.