Dynamic diffraction and interband transitions in two-dimensional photonic lattices

We reveal a direct link between two fundamental wave phenomena in periodic media, Pendell?sung oscillations and resonant coupling between spectral bands. We experimentally measure the power transfer between laser beams associated with the high-symmetry points in periodic and biased hexagonal photonic lattices. As a result, we demonstrate that Pendell?sung oscillations dominate the dynamics of resonant interband transitions on a short propagation scale.     

Multimode nematicon waveguides

We report on the first (to our knowledge) experimental observation of higher-order modes guided by soliton-induced waveguides in nematic liquid crystals. We find that the nematicon waveguides operate in a bounded power region specific to each guided mode. Below this region, the guided beams diffract; above this region, the mode mixing and coupling give rise to an unstable output.     

Energetics and mechanisms for the unimolecular dissociation of protonated trioses and relationship to proton-mediated formaldehyde polymerization to carbohydrates in interstellar environments

We report the unimolecular decomposition of protonated glyceraldehyde, [HOCH(2)CH(OH)CHO]H(+), and protonated dihydroxyacetone, [HOCH(2)C(O)CH(2)OH]H(+). On the basis of mass spectrometric experiments and computational quantum chemistry, we have found that these isomeric ions interconvert freely at energies below that required for their unimolecular decompositions. The losses of formaldehyde and water (the latter also followed by CO loss) are the dominating processes, with formaldehyde loss having the lower energetic threshold. The reverse of the formaldehyde loss, namely, the addition of formaldehyde to protonated glycolaldehyde, appears to be an inefficient reaction at low temperature and pressure in the gas phase, leading to dissociation products. The relevance of these findings to interstellar chemistry and prebiotic chemistry is discussed, and it is concluded that the suggestion made in the literature that successive addition of formaldehyde by proton-assisted reactions should account for interstellar carbohydrates most likely is incorrect.     

Emissive metallomesogens based on 2-phenylpyridine complexes of iridium(III)

Preparation of Ir(III) complexes using anisotropic 2,5-di(4-alkoxyphenyl)pyridine ligands leads to emissive, liquid-crystalline complexes containing bound Cl and dimethyl sulfoxide. Using analogous poly(alkoxy) ligands allows the preparation of bis(2-phenylpyridine)iridium(III) acac complexes, which are also mesomorphic. The observation of liquid crystallinity in octahedral complexes of this type is without precedent.     

Chain-growth polymerization of unusual anion-radical monomers based on naphthalene diimide: a new route to well-defined n-type conjugated copolymers

Strongly electron-deficient (n-type) main-chain π-conjugated polymers are commonly prepared via well-established step-growth polycondensation protocols which enable limited control over polymerization. Here we demonstrate that activated Zn and electron-deficient brominated thiophene-naphthalene diimide oligomers form anion-radical complexes instead of conventional Zn-organic derivatives. These highly unusual zinc complexes undergo Ni-catalyzed chain-growth polymerization leading to n-type conjugated polymers with controlled molecular weight, relatively narrow polydispersities, and specific end-functions.     

Thermophysical study of graphene nanoflakes by differential scanning calorimetry

Journal of Thermal Analysis and Calorimetry - Combustion heats of graphene nanoflakes (GNFs) of different thicknesses produced by chemical vapor deposition method were measured for the first time...     

The perspectives of ethanol usage as an internal standard for the quantification of volatile compounds in alcoholic products by GC‐MS

The potential use of ethanol as an internal standard (IS) for GC‐MS analysis was studied. The paper describes the analysis of spirit drinks and other alcoholic products which consist of a mixture of water, ethanol, and volatile compounds. In the suggested method, ethanol was employed as an IS for the common procedure of volatile compounds quantification. A number of standard solutions of nine compounds with different concentrations was prepared in a water‐ethanol matrix and measured with GC‐MS in the SIM mode. Two possible approaches were suggested to avoid detector saturation during ethanol detection. The first one consisted in using less abundant m/z 47 as quantifiers. These ions mainly correspond to unfragmented heavy ethanol molecules containing one ¹³C isotope. The second method consisted in reduction of the voltage of MS electron multiplier. The experiment also included the preparation and subsequent dilution of the standard solution and ethanol with water, which determined the linearity of the modified MS response relative to the ethanol content. Analysis of the obtained results revealed that volatile compounds can be successfully accurately determined with GC‐MS by employing ethanol as an IS. Application of the suggested method is not limited to the reported volatile compounds and alcoholic products.     

A Room‐Temperature Verwey‐type Transition in Iron Oxide,Fe5O6

Functional oxides whose physicochemical properties may be reversibly changed at standard conditions are potential candidates for the use in next‐generation nanoelectronic devices. To date, vanadium dioxide (VO₂) is the only known simple transition‐metal oxide that demonstrates a near‐room‐temperature metal–insulator transition that may be used in such appliances. In this work, we synthesized and investigated the crystals of a novel mixed‐valent iron oxide with an unconventional Fe₅O₆ stoichiometry. Near 275 K, Fe₅O₆ undergoes a Verwey‐type charge‐ordering transition that is concurrent with a dimerization in the iron chains and a following formation of new Fe?Fe chemical bonds. This unique feature highlights Fe₅O₆ as a promising candidate for the use in innovative applications. We established that the minimal Fe?Fe distance in the octahedral chains is a key parameter that determines the type and temperature of charge ordering. This model provides new insights into charge‐ordering phenomena in transition‐metal oxides in general.