Dendrimer molecules with record large two-photon absorption cross section

We report what is to our knowledge a record high value for an intrinsic two-photon absorption (TPA) cross section, sigma(2) = 11 x 10(-47)> cm>(4)> s photon(-1) molecule(-1), measured with femtosecond pulses in a new dendrimer molecule comprising 29 repeat units of 4, 4(?)-bis(diphenylamino)stilbene chromophore. We measure the dependence of TPA on excitation wavelength in three consecutive generations of the dendrimer and show that the maximum sigma(2) value increases faster than the total number of stilbene chromophores. This result indicates that it is possible to obtain even larger sigma(2) values in higher generations of this dendrimer family.     

用于ECR离子源的超导磁体——设计与制造

Superconducting magnets are widely used in ECR ion sources.The intensity and form of the magnetic field plays an important role in the way towards higher performance sources.During the development steps,the design principles and geometries had to be adapted to reach higher fields using state-of-the-art technologies and design tools.Production,assembly,and tests of these superconducting magnets are presented and a short outlook on possible future developments is given.     

X=Y-ZH Systems as potential 1,3-dipoles : Part 13. Prototropic generation of azomethine imines from hydrazones

Hydrazones of aldehydes and ketones undergo intermolecular cycloaddition to electronegative olefins via azomethine imines, formed by a formal 1,2-prototropic shift, in low to moderate yield on heating in xylene or ethanol. In some instances the reaction is diverted to give products derived (at least formally) from an ene reaction. Similar intramolecular cycloadditions occur with unactivated terminal alkenes and alkynes.     

Thermal analysis of cobalt,nickel and copper complexes of 2-aminothiazole

The thermal decomposition of 2-aminothiazole (2-amt) complexes of general formula M(2-amt)₂X₂ [M = Co(II) and Cu(II)] and Ni(2-amt)₄X₂ [X = Cl and Br] have been studied in air and argon by TG and DTG as well as by DTA in nitrogen; end products from the decompositions in air have been characterised by X-ray powder diffraction. Decomposition stoichiometries have been proposed and factors governing the thermal decomposition have been discussed.     

Investigation of free base, Mg, Sn, and Zn substituted porphyrin LB films as gas sensors for organic analytes

The visible absorption spectra of various substituted porphyrin compounds both in chloroform solution and as Langmuir-Blodgett (LB) solid-state films have been investigated. The porphyrin compounds examined were the Zn, Sn, Mg, and free base derivatives of 5,10,15,20-tetrakis[3,4-bis(2-ethylhexyloxy)phenyl]-21H,23H-porphine (EHO). Changes in the absorption spectra of these materials induced by their exposure to various organic compounds are reported with a view toward determining whether this is a useful approach toward an optical gas sensor.     

Investigation of solvatochromism in the low-lying singlet states of dithienyl polyenes

To understand the low-lying singlet states of dithienyl polyenes, we investigated the solvatochromism of a series of α,ω-di(2-dithienyl 3,4-butyl) polyenes having n=1–5 double bonds. Absorption and emission spectra were collected in a series of aprotic solvents. The absorption energy dispersion effect sensitivity increased smoothly with n, reaching asymptotic behavior as n approached 5. The emission energy had less solvent sensitivity. The trends gave evidence for the existence of a ¹B^*_u absorbing state and a ¹A^*_g emitting state. We observed sensitivity of the absorbing and emitting states to solute–solvent electrostatic interactions, suggesting the dithienyl polyenes had a polar ground state conformation.     

Molecular dynamics simulations of the thermal conductivity of methane hydrate

Nonequilibrium molecular dynamics simulations with the nonpolarizable SPC/E (Berendsen et al., J. Phys. Chem. 1987, 91, 6269) and the polarizable COS/G2 (Yu and van Gunsteren, J. Chem. Phys. 2004, 121, 9549) force fields have been employed to calculate the thermal conductivity and other associated properties of methane hydrate over a temperature range from 30 to 260 K. The calculated results are compared to experimental data over this same range. The values of the thermal conductivity calculated with the COS/G2 model are closer to the experimental values than are those calculated with the nonpolarizable SPC/E model. The calculations match the temperature trend in the experimental data at temperatures below 50 K; however, they exhibit a slight decrease in thermal conductivity at higher temperatures in comparison to an opposite trend in the experimental data. The calculated thermal conductivity values are found to be relatively insensitive to the occupancy of the cages except at low (T相似文献   

1-diphenylphosphinyl-2,2-dimethylaziridine - a new precursor of α,α-dimethylarylalkylamines

The new synthesis of α,α-dimethylarylalkylamines from 1-diphenylphosphinyl-2,2-dimethylaziridine is described.     

Constructing orthogonal pandiagonal Latin squares and panmagic squares from modular n‐queens solutions

In this article, we show how to construct pairs of orthogonal pandiagonal Latin squares and panmagic squares from certain types of modular n‐queens solutions. We prove that when these modular n‐queens solutions are symmetric, the panmagic squares thus constructed will be associative, where for an n × n associative magic square A = (a_ij), for all i and j it holds that a_ij + an?i?1,n?j?1 = c for a fixed c. We further show how to construct orthogonal Latin squares whose modular difference diagonals are Latin from any modular n‐queens solution. As well, we analyze constructing orthogonal pandiagonal Latin squares from particular classes of non‐linear modular n‐queens solutions. These pandiagonal Latin squares are not row cyclic, giving a partial solution to a problem of Hedayat. © 2007 Wiley Periodicals, Inc. J Combin Designs 15: 221–234, 2007