Peri-Decoration of a Tetraazaperylene with Urea Units: Chiral Octaazaperopyrenedioxides (OAPPDOs) and Their Optical and Chiroptical Properties

Octaazaperopyrenedioxides (OAPPDOs) are a new class of fluorescent polycyclic aromatic hydrocarbons based on a tetraazaperylene core that is formally condensed with N-substituted urea units in the two opposite peri positions. Here, we report the synthesis of series of substituted OAPPDO derivatives with different N-substitution patterns (H, alkyl, benzyl) in the peri positions, including bay-chlorinated OAPPDOs. Starting from the latter, a series of bay-arylated OAPPDOs was synthesized by Suzuki cross coupling, which resulted in the formation of helically chiral OAPPDO derivatives. The electrochemical and photophysical properties were investigated by UV/Vis and fluorescence spectroscopy as well as cyclic voltammetry. The P and M enantiomers of a phenylated OAPPDO were separated by semipreparative HPLC and further analyzed by CD spectroscopy. The frontier orbital energies, the mechanism of the isomerization, the electronic excitation and the CD spectrum (TD-DFT) were computed and compared to the experimental data. The reversible 1e⁻ oxidation of the OAPPDOs generates the corresponding radical cations, one of which was characterized by EPR spectroscopy. The reversible oxidation process was also systematically investigated by spectro-electrochemistry.     

Amide Synthesis by Nickel/Photoredox-Catalyzed Direct Carbamoylation of (Hetero)Aryl Bromides

Herein, we report a one-electron strategy for catalytic amide synthesis that enables the direct carbamoylation of (hetero)aryl bromides. This radical cross-coupling approach, which is based on the combination of nickel and photoredox catalysis, proceeds at ambient temperature and uses readily available dihydropyridines as precursors of carbamoyl radicals. The method's mild reaction conditions make it tolerant of sensitive-functional-group-containing substrates and allow the installation of an amide scaffold within biologically relevant heterocycles. In addition, we installed amide functionalities bearing electron-poor and sterically hindered amine moieties, which would be difficult to prepare with classical dehydrative condensation methods.     

Eddy-Viscosity and Stress-Transport Turbulence Models in Application to a Plane Synthetic Jet

A two-dimensional unsteady plane jet is computed using four turbulence models. The strain field generated by the ‘synthetic’ (reciprocating) jet under consideration contains regions of strong normal and shear straining, while vortex pairs formed by the issuing jet are highly rotational. Turbulence closures at the eddy-viscosity level (standard k???ε and two-timescale models) and two stress-transport closures (the ‘basic’ model and a two-component-limit scheme) are examined against experimental data. It is found that the extreme nature of the strain environment presents a severe challenge to the models tested; in particular, fundamental weaknesses in the constitutive equation of linear eddy viscosity models are highlighted. An additional term in the dissipation rate equation of the two-timescale model is found to hinder the formation of clearly defined starting vortex pairs which play a critical role in determining the near-field pattern of synthetic jet development. The stress-transport models are able to reproduce measured turbulence quantities with a greater degree of accuracy, and the two-component-limit formulation shows an improvement over the basic model.     

Mapping forces in a 3D elastic assembly of grains

Our understanding of the elasticity and rheology of disordered materials, such as granular piles, foams, emulsions or dense suspensions relies on improving experimental tools to characterise their behaviour at the particle scale. While 2D observations are now routinely carried out in laboratories, 3D measurements remain a challenge. In this paper, we use a simple model system, a packing of soft elastic spheres, to illustrate the capability of X-ray microtomography to characterise the internal structure and local behaviour of granular systems. Image analysis techniques can resolve grain positions, shapes and contact areas; this is used to investigate the material's microstructure and its evolution upon strain. In addition to morphological measurements, we develop a technique to quantify contact forces and estimate the internal stress tensor. As will be illustrated in this paper, this opens the door to a broad array of static and dynamical measurements in 3D disordered systems.     

Activity coefficients at infinite dilution of hydrocarbons,alkylbenzenes, and alcohols in the paramagnetic ionic liquid 1-butyl-3-methyl-imidazolium tetrachloridoferrate(III) using gas–liquid chromatography

Activity coefficients at infinite dilution ${\gamma }_i^{\infty }$ of alkanes, alkenes, and alkylbenzenes as well as of the linear C₁–C₆ alcohols in the paramagnetic ionic liquid 1-butyl-3-methyl-imidazolium tetrachloridoferrate(III) have been determined by gas chromatography using the ionic liquids as stationary phase. The measurements were carried out at different temperatures between (305 and 403) K. From the temperature dependence of the limiting activity coefficients partial molar excess enthalpies at infinite dilution $H_i^{E\text{,}\infty }$ of the solutes in the ionic liquids have been derived. Activity coefficients at infinite dilution ${\gamma }_i^{\infty }$ of ionic liquid with the ionic liquids containing 1-butyl-3-methyl-imidazolium cation and different non-magnetic anions have been compared at 298 K with results for 1-butyl-3-methyl-imidazolium tetrachloridoferrate(III). No significant effects caused by the paramagnetic anion anion have been observed.     

Tight sets and <Emphasis Type="Italic">m</Emphasis>-ovoids of generalised quadrangles

The concept of a tight set of points of a generalised quadrangle was introduced by S. E. Payne in 1987, and that of an m-ovoid of a generalised quadrangle was introduced by J. A. Thas in 1989, and we unify these two concepts by defining intriguing sets of points. We prove that every intriguing set of points in a generalised quadrangle is an m-ovoid or a tight set, and we state an intersection result concerning these objects. In the classical generalised quadrangles, we construct new m-ovoids and tight sets. In particular, we construct m-ovoids of W(3,q), q odd, for all even m; we construct (q+1)/2-ovoids of W(3,q) for q odd; and we give a lower bound on m for m-ovoids of H(4,q ²).