Two-photon absorption and third-order nonlinear optical characterization of pyrrolo-tetrathiafulvalene derivatives

To provide an insight into the third-order nonlinear optical (NLO) behaviour of a series of tetrathiafulvalene (TTF)-based molecules, the third-order NLO properties and two-photon absorption characterizations have been theoretically investigated by means of the time-dependent Hartree–Fock method. According to ab-initio calculation results, the examined molecules exhibit second hyperpolarizabilities $(\gamma )$ with non-zero values, implying microscopic third-order optical nonlinearity. Our computed results are also in good agreement with the previous experimental observations on the title compounds.     

Interpretations of cosmological spectral shifts

It is shown that for Robertson-Walker models with flat or closed space sections, all of the cosmological spectral shift can be attributed to the non-flat connection (and thus indirectly to space-time curvature). For Robertson-Walker models with hyperbolic space sections, it is shown that cosmological spectral shifts uniquely split up into “kinematic” and “gravitational” parts provided that distances are small. For large distances no such unique split-up exists in general. A number of common, but incorrect assertions found in the literature regarding interpretations of cosmological spectral shifts, is pointed out.     

On some sharp bounds for the homogenized p-poisson equation

We consider homogenization of a scale of p-Poisson equations in R^N. Some new bounds of the effective energy are proved and compared with the non-linear Wiener -and Hashin-Shtrikman bounds. Moreover, we point out concrete nontrivid examples where these bounds even coincide. Some new examples of “optimal” microstructures are presented.     

The ability of a novel sorptive polymer to determine the freely dissolved fraction of polar organic compounds in the presence of fulvic acid or sediment

A novel plastic material, poly(ethylene-co-vinyl acetate-co-carbon monoxide) (PEVAC), was evaluated as an absorptive passive equilibrium sampler for determination of the freely dissolved fraction of seven polar organic contaminants (POCs) in the presence of fulvic acid and sediment. The seven compounds selected were imidacloprid, carbendazim, metoprolol, atrazin, carbamazepine, diazinon and chlorpyrifos, i.e. a mixture of pharmaceuticals and pesticides having logarithmic octanol/water partition coefficients (log K _OW) ranging from 0.2 to 4.77. The experiments demonstrated that the PEVAC sampler is well suited for determination of the freely dissolved fraction of chemicals in aquatic environments. Generally, the freely dissolved fraction of the POCs decreased with increasing hydrophobicity. However, strong interactions with functional groups of the organic matter seemed to dominate the partitioning for imidacloprid and carbendazim, having logarithmic dissociation partition coefficient log D < 1.47, and for metoprolol, which is positively charged at neutral pH.     

The phase transition of two-dimensional squaric acid H2C4O4 studied by neutron scattering

At T_c = 370 K squaric acid undergoes a phase transition, which was studied in detail by neutron scattering. The transition is essentially two-dimensional with β = 0.137 ± 0.010. Diffuse scattering above T_e is found to be anisotropic. From “diffuse crystallography” it is concluded that proton disorder is not the dominant source of diffuse scattering. Individual molecules retain their low-temperature shape in the high-temperature phase.     

The interaction of 1,1'-diisocyanoferrocene with gold: formation of monolayers and supramolecular polymerization of an aurophilic ferrocenophane

The coordination chemistry of 1,1'-diisocyanoferrocene (1) was investigated. Its reaction with Cr(CO)5(THF) (2 equiv) affords (1)[Cr(CO)5]2, which exhibits eclipsed cyclopentadienyl rings with a synclinal arrangement of the two substituents. 1 behaves like an aryl isocyanide in this compound according to IR spectroscopic data, and its oxidation leads to a marked decrease of net electron donor ability. The reaction of 1 with AuCl(SMe2) affords the insoluble coordination polymer [(1)(AuCl)2]infinity. The (1)(AuCl)2 molecules adopt a 3,4-diaura-[6]ferrocenophane structure. They are aggregated in a zipperlike fashion through aurophilic interactions, with Au-Au distances ranging from 3.34 to 3.48 A. The adsorption of 1 from acetonitrile solution on polycrystalline gold affords a self-assembled monolayer. Both isocyanide groups are binding to the surface.     

Crystalline-crystalline block copolymers of regioregular poly(3-hexylthiophene) and polyethylene by ring-opening metathesis polymerization

Block copolymers of regioregular poly(3-hexylthiophene) (P3HT) and polyethylene (PE) were synthesized through the chain transfer of olefin-terminated P3HT in the presence of cyclooctene via ring-opening metathesis polymerization (ROMP). Subsequent hydrogenation of the poly(cyclooctene) block yielded high molecular weight, crystalline-crystalline P3HT-PE block copolymers, which are thermally stable and resistant to solvents under ambient conditions. These copolymers were characterized by 1H NMR, DSC, and WAXS and represent the first materials of a class of crystalline-crystalline semiconducting-insulating block copolymers.     

Ultrathin films of semiconducting polymers on water

Ultrathin films of polythiophene derivatives spread on water were studied by means of synchrotron radiation, using grazing incidence diffraction and (specular) reflectometry to obtain the molecular orientation in the films. The semicrystalline films were anisotropic, showing a strong tendency of orienting the crystalline alpha-axis perpendicularly to the water subphase. The crystalline domains extend essentially through the entire sample thickness, found to be 10-15 nm. A large expansion of the unit cell alpha-parameter was seen upon doping the films in situ. The reflectometry data were well-fitted by a model with a sinusoidal density variation being damped toward the water subphase. This indicates that the crystalline order was most developed at the polymer-air interface and deteriorated down toward the water, possibly due to the hydrophobicity of the alkyl side chains.     

Measuring deviations from stationarity

Various parameters for measuring the deviation from stationarity for processes belonging to two classes of nonstationarity processes are proposed. Several new results for the two types of processes are obtained. Points of contact are established with the class of oscillatory processes and with the Hamiltonian equation of motion in quantum mechanics. The relation to processes of normal type and to innovations stable processes is also discussed.     

In situ studies of phase transitions in thin discotic films

The crystalline to liquid crystalline (Cr-LC) phase transition in thin films of zone-cast hexa-peri-hexabenzocoronene sixfold substituted with dodecyl side chains (HBC-C12H25) has been studied in detail using grazing incidence X-ray diffraction (GID), electron diffraction (ED), and variable angle spectroscopic ellipsometry (VASE), When heating the material, a first minor transition is observed around 42 degrees C. This change is attributed to alterations of the crystalline alkyl chain packing, which only slightly changes the electronic properties of the material. At higher temperatures of about 90 degrees C, but still significantly below the previously reported transition temperature in bulk, the Cr-LC transition is observed. An accompanying large increase in optical anisotropy is compatible with the X-ray data, showing a transition from the as-cast herringbone-like crystalline state to a highly ordered discotic hexagonal columnar LC phase. The structural transition has the macroscopic effect of increasing the film thickness. The high structural order of the as-cast low-temperature phase is only partly recovered after cooling, and the phase transition exhibits a large hysteresis. From the ellipsometry data, the dielectric tensor of HBC-C12H25 was refined to unprecedented detail.