ANION AND SOLVENT EFFECTS ON THE RATE OF REDUCTION OF TRIPLET EXCITED THIAZINE DYES BY FERROUS IONS

Abstract— The lifetimes of the triplet excited states of thionine and methylene blue were measured in aqueous and 50 v/v% aqueous acetonitrile solutions acidified with 0.01 N sulfuric or trifluoromethyl-sulfonic acid. The rate constants for reaction of the triplet excited dyes with ferrous ions were measured in the same solutions. The triplet lifetimes in the absence of added quenchers were insensitive to a change in acid from trifluoromethylsulfonic to sulfuric or to a change in solvent from water to 50v/v% aqueous acetonitrile (τ for triplet thionine ˜7.5 μs, τ for triplet methylene blue ˜4.5 μs). In contrast, the rate constant for reaction of the triplet dyes with ferrous ions increased by nearly a factor of 10 with a change in acid from trifluoromethylsulfonic to sulfuric. In solutions containing sulfate ions this reaction rate constant increased with increasing sulfate concentration and with a change in solvent from water to 50 v/v% aqueous acetonitrile. The results are discussed in terms of the possibility of association of the positively charged reactive ions with sulfate anions. Quenching of the triplet excited dyes by ferric ions or by ground state dye molecules was shown to be negligible at the concentration used for the ferrous ion quenching study.     

Ma?analytische Bestimmung des Quecksilbers

Ohne Zusammenfassung     

Nachweis und Bestimmung der Halogene

Ohne Zusammenfassung     

Analyse von Bleilegirungen

Ohne Zusammenfassung     

Conformational landscapes of bimesogenic compounds and their implications for the formation of modulated nematic phases

ABSTRACT

The twist-bend phase (N_TB) is most commonly observed in materials with a gross-bent shape: dimers; bent-cores; bent-oligomers. We had suggested previously that the bend-angle of such systems effectively dictates the relative thermal stability of the N_TB phase. However, our earlier paper relied on the use of a single energy-minimum conformer and so failed to capture any information about flexibility and conformational distribution. In the present work, we revisit our hypothesis and examine a second set of dimers with varying linking groups and spacer composition. We have improved on our earlier work by studying the conformational landscape of each material, allowing average bend-angles to be determined as well as the conformer distribution. We observe that the stability of the N_TB phase exhibits a strong dependence not only on the Boltzmann-weighted average bend-angle (rather than just a static conformer), but also on the distribution of conformers. To a lesser extent, the flexibility of the spacer appears important. Ultimately, this work satisfies both theoretical treatments and our initial experimental study and demonstrates the importance of molecular bend to the N_TB phase.     

Synthesis,characterization, and blends of high temperature poly(arylether sulfone)s

The preparation of poly(4-oxy-1,4-phenylenesulfonyl-4,4′-biphenylene-4-sulfonylphenylene) (PBP) has been accomplished by the base mediated, polycondensation reaction between two biphenyl containing monomers. The bisphenol, 4,4′-bis[(4-hydroxyphenyl) sulfonyl]biphenyl (HSB), was reacted with 4,4′-bis[(4-chlorophenyl)sulfonyl]-biphenyl (CSB) in tetramethylene sulfone solvent. The highest mechanical properties and glass transition temperature was observed for polymer PBP with a reduced viscosity around 1.0 dL/g. Consequently, the current synthesis route provides polymer with higher properties than other historical preparative routes. Blends of PBP with a different poly(ether sulfone) were miscible based on the observance of a single glass transition temperature. The T_gs of the polymer blends exhibited an unusual positive deviation from the weighted linear averages of the components.     

ChemInform Abstract: Matrix Infrared Spectroscopic and Theoretical of the Difluoroamino Metal Fluoride Molecules: F2NMF (M: Cu,Ag, Au).

The title molecules are obtained from spontaneous reactions of coinage metals and NF₃ in solid Ar and Ne matrices.     

ChemInform Abstract: Infrared Spectroscopic and Theoretical Investigations of the OUF2 and OThF2 Molecules with Triple Oxo Bond Character.

The title molecules are prepared by reaction of OF₂ molecules with laser ablated uranium and thorium atoms in solid argon and neon.