Synthesis and Photophysical Properties of 1,1,4,4-Tetracyanobutadienes Derived from Ynamides Bearing Fluorophores**

1,1,4,4-Tetracyanobutadienes (TCBDs) bearing a large diversity of fluorophores were prepared following a multi-step synthesis. In a crucial last step, all compounds were obtained from the corresponding ynamides, which were particularly suitable for the formation of the TCBDs in the presence of tetracyanoethylene via a [2+2] cycloaddition/retroelectrocyclization step (CA-RE). Several fluorenyl derivatives in addition to phenanthrenyl and terphenyl ones provided ynamide-based TCBDs affording remarkable emission properties covering a large range of wavelengths. Those compounds emit both in solid state and in solution from the visible region to the NIR range, depending on the molecular structures. Quantum yields in cyclohexane reached unforeseen values for such derivatives, up to 7.8 %. A huge sensitivity to the environment of the TCBDs has also been unraveled for most of the compounds since we observed a dramatic fall of the quantum yields when changing the solvent from cyclohexane to toluene, while they are almost non-emissive in dichloromethane.     

Nonlinear vibration localisation in a symmetric system of two coupled beams

Nonlinear Dynamics - We report nonlinear vibration localisation in a system of two symmetric weakly coupled nonlinear oscillators. A two degree-of-freedom model with piecewise linear stiffness...     

Straightforward Ball-Milling Access to Dinucleoside 5′,5′-Polyphosphates via Phosphorimidazolide Intermediates

A solvent-assisted mechanochemical approach to access symmetrical and mixed dinucleoside 5,5′-polyphosphates is reported. Under ball-milling conditions, nucleoside 5′-monophosphates were quantitatively activated using 1,1′-carbonyldiimidazole, forming their phosphorimidazolide derivatives. The addition of a nucleoside 5′-mono-, di- or triphosphate directly led to the formation of the corresponding dinucleotides. Benefits of the reported one-pot method include the use of unprotected nucleotides in their sodium or acid form, activation by the eco-friendly 1,1′-carbonyldiimidazole, non-dry conditions, short reaction time, high conversion rates, and easy setup and purification. This work offers new perspectives for the synthesis of nucleotide conjugates and analogues, combining the phosphorimidazolide approach and milling conditions.     

Optimal Market Dealing Under Constraints

We consider a market dealer acting as a liquidity provider by continuously setting bid and ask prices for an illiquid asset in a quote-driven market. The market dealer may benefit from the bid–ask spread, but has the obligation to permanently quote both prices while satisfying some liquidity and inventory constraints. The objective is to maximize the expected utility from terminal liquidation value over a finite horizon and subject to the above constraints. We characterize the value function as the unique viscosity solution to the associated Hamilton–Jacobi–Bellman equation, and further enrich our study with numerical results. The contributions of our study concern both the modelling aspects and the dynamic structure of the control strategies. Important features and constraints characterizing market making problems are no longer ignored.     

Simple Access to Highly Functional Bicyclic γ‐ and δ‐Lactams: Origins of Chirality Transfer to Contiguous Tertiary/Quaternary Stereocenters Assessed by DFT

This paper describes the synthesis of both polysubstituted oxazolo‐pyrrolidinones and ‐piperidinones by a domino process. The methodology is based on the reaction between hydroxyl halogenoamides and Michael acceptors, which leads efficiently to bicyclic lactams. The process is compatible with unsymmetrical electron‐withdrawing groups on the Michael acceptor, which allows the formation of two contiguous and fully controlled tertiary and quaternary stereocenters. In the case of tetrasubstituted Michael acceptors, two adjacent quaternary stereocenters are formed in good yield. Starting from (R)‐phenylglycinol derived amides results in the formation of enantioenriched bicyclic lactams in low to good yields and with high levels of stereoselectivity, thus greatly increasing the scope and interest of this strategy. The origins of chirality transfer and diastereoselectivity were studied by DFT calculations and have been attributed to a kinetic control in one of the last two steps of the reaction sequence. This selectivity is dependent upon both the substituents on the Michael acceptor and the sodium cation chelation.     

Rheological and electrical properties of EVA copolymer filled with bamboo charcoal

The electrical and rheological properties of an ethylene vinyl acetate (EVA) copolymer filled with bamboo charcoal were investigated. The composites were prepared by melt process in an internal batch mixer. Size distribution analysis showed that d₍₅₀₎ and d₍₉₀₎ values of the bamboo charcoal particles are 12.7 and 40 μm, respectively, with a mean diameter of 22 μm. Scanning electron microscopy proved that the particles of bamboo charcoal present a rectangular shape. The electrical percolation threshold was observed at 0.18 volume fraction (35 wt%) of bamboo. Beyond the percolation threshold, a considerable increase in electrical properties was observed up to a limit value of 10^-2 S/m. The rheological percolation was studied from different rheological models. As a result, the rheological percolation threshold was observed at 0.3 volume fraction (50 wt%) of bamboo charcoal contents. So, the electrical percolation occurs before the rheological percolation. This is principally due to the filler’s characteristics such as the specific surface area, the aspect ratio, and the surface properties. Finally, the bamboo charcoal confers high electrical properties to the EVA composite without inducing strong changes in its viscoelastic properties.     

Directive metamaterial-based subwavelength resonant cavity antennas – Applications for beam steering

This article presents the use of composite resonant metamaterials for the design of highly directive subwavelength cavity antennas. These metamaterials, composed of planar metallic patterns periodically organized on dielectric substrates, exhibit frequency dispersive phase characteristics. Different models of metamaterial-based surfaces (metasurfaces), introducing a zero degree reflection phase shift to incident waves, are firstly studied where the bandwidth and operation frequency are predicted. These surfaces are then applied in a resonant Fabry–Perot type cavity and a ray optics analysis is used to design different models of ultra-compact high-gain microstrip printed antennas. Another surface presenting a variable reflection phase by the use of a non-periodic metamaterial-based metallic strips array is designed for a passive low-profile steering beam antenna application. Finally, the incorporation of active electronic components on the metasurfaces, allowing an electronic control of the phase responses, is applied to an operation frequency reconfigurable cavity and a beam steering cavity. All these cavity antennas operate on subwavelength modes, the smallest cavity thickness being of the order of λ/60. To cite this article: A. Ourir et al., C. R. Physique 10 (2009).