An Efficient Synthesis of 2,3,5,6-Tetramethylidene-7-oxanorbornane

Palladium-catalyzed double carbomethoxylation of the Diels-Alder adduct of furan and maleic anhydride yielded the methyl all-exo-7-oxanorbornane-2,3,5,6-tetracarboxylate (7) which was transformed in three steps into 2,3,5,6-tetramethylidene-7-oxanorbornane (1) , a useful synthon. Six isomeric methyl 7-oxanor-bornane-2,3,5,6-tetracarboxylates (7–12) have been isolated and their ¹H- and ¹³C-NMR. data are compared.     

Synthesis of Branched Polymers under Continuous‐Flow Microprocess: An Improvement of the Control of Macromolecular Architectures

Polymerization reactions can benefit from continuous‐flow microprocess in terms of kinetics control, reactants mixing or simply efficiency when high‐throughput screening experiments are carried out. In this work, we perform for the first time the synthesis of branched macromolecular architecture through a controlled/‘living' polymerization technique, in tubular microreactor. Just by tuning process parameters, such as flow rates of the reactants, we manage to generate a library of polymers with various macromolecular characteristics. Compared to conventional batch process, polymerization kinetics shows a faster initiation step and more interestingly an improved branching efficiency. Due to reduced diffusion pathway, a characteristic of microsystems, it is thus possible to reach branched polymers exhibiting a denser architecture, and potentially a higher functionality for later applications.     

Synthesis and Thin Film Phase Behaviour of Functional Rod‐Coil Block Copolymers Based on Poly(para‐phenylenevinylene) and Poly(lactic acid)

We report the synthesis of a series of block copolymers consisting of a rod‐like semiconducting poly(2,5‐di(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene) (DEH‐PPV) block and a flexible poly(lactic acid) (PLA) block that can be selectively degraded under mild conditions. Such selectively degradable block copolymers are designed as self‐assembling templates for bulk heterojunction donor–acceptor layers in organic solar cells. A lamellar microphase‐separated domain structure was identified for block copolymers with PLA volume fractions between 29 and 79% in bulk and thin films using SAXS, TEM, and AFM. Depending on the ratio of the two blocks we find either lamellae oriented parallel or perpendicular to the substrate in thin films.

     

‘All‐supramolecular’ Nanocapsules from Low‐Molecular Weight Ureas Through Interfacial Addition Reaction in Miniemulsion

This contribution presents a new strategy for preparing nanocapsules with a shell made of a supramolecular polymer which repeating units are held together by reversible interactions rather than covalent bonds. These nanocapsules were prepared in classical miniemulsion through interfacial addition reaction of a diisocyanate (IPDI) and a monoamine (iBA), forming low‐molecular weight bis‐ureas moieties which are strong self‐complementary interacting molecules through hydrogen‐bonding. The nanocapsules present a diameter around 100 nm, and MALDI‐TOF MS and ¹H NMR analyses confirm the expected molecular characteristics for the shell. This strategy opens the scope of a new type of nanomaterials exhibiting stimuli‐responsiveness due to the reversible interaction linking the repeating units.

     

On the clarification of the IR stretching vibration assignment of adsorbed N2 on Rh0 and Rhdelta+ surface atoms of supported Rh crystallites

The low-temperature adsorption of N(2) on Rh/SiO(2) samples of various particle-size distributions was followed by FTIR. The addition of O(2) pulses on Rh(0) surfaces saturated with chemisorbed N(2) allowed us to reassign stretching frequencies attributed originally to N(2)-Rh(0) to N(2)-Rh(delta+). The formation of the latter oxidized Rh species is assumed to be induced by an electron withdrawal from adsorbed oxygen species on Rh surface centers neighboring those onto which N(2) species are chemisorbed. The present work, thus, enables us to delimit ranges of frequencies for which the adsorption of N(2) can be considered to occur on either Rh(0) or Rh(delta+) centers for nu(N2) lower or higher than 2243 cm(-1), respectively. The N(2)-FTIR experiments performed on the studied catalysts also suggest a lattice plane selectivity for N(2) adsorption on metallic Rh planes of different natures which, to our knowledge, has not been reported yet for Rh.     

Preparation of annulated nitrogen-containing heterocycles via a one-pot palladium-catalyzed alkylation/direct arylation sequence

[reaction: see text] A palladium-catalyzed/norbornene-mediated sequential coupling reaction involving an aromatic sp(2) C-H functionalization as the key step is described, in which an alkyl-aryl bond and an aryl-heteroaryl bond are formed in one pot. A variety of highly substituted six- and seven-membered annulated pyrroles and pyrazoles were synthesized in a one-step process in good yields from readily accessible N-bromoalkyl pyrroles or pyrazoles and aryl iodides.     

Optical properties of individual manganese-doped quantum dots

The magnetic state of a single magnetic ion (Mn²⁺) embedded in an individual quantum dot is optically probed using micro-spectroscopy. The fine structure of a confined exciton in the exchange field of a single Mn²⁺ ion (S=) is analyzed in detail. The exciton–Mn²⁺ exchange interaction shifts the energy of the exciton depending on the Mn²⁺ spin component and six emission lines are observed at zero magnetic field. The emission spectra of individual quantum dots containing a single magnetic Mn atom differ strongly from dot to dot. The differences are explained by the influence of the system geometry, specifically the in-plane asymmetry of the quantum dot and the position of the Mn atom. Depending on both these parameters, one has different characteristic emission features which either reveal or hide the spin state of the magnetic atom. The observed behavior in both zero field and under magnetic field can be explained quantitatively by the interplay between the exciton–Mn²⁺ exchange interaction (dependent on the Mn position) and the anisotropic part of the electron–hole exchange interaction (related to the asymmetry of the quantum dot).     

Statistical properties of subgroups of free groups

The usual way to investigate the statistical properties of finitely generated subgroups of free groups, and of finite presentations of groups, is based on the so‐called word‐based distribution: subgroups are generated (finite presentations are determined) by randomly chosen k ‐tuples of reduced words, whose maximal length is allowed to tend to infinity. In this paper we adopt a different, though equally natural point of view: we investigate the statistical properties of the same objects, but with respect to the so‐called graph‐based distribution, recently introduced by Bassino, Nicaud and Weil. Here, subgroups (and finite presentations) are determined by randomly chosen Stallings graphs whose number of vertices tends to infinity. Our results show that these two distributions behave quite differently from each other, shedding a new light on which properties of finitely generated subgroups can be considered frequent or rare. For example, we show that malnormal subgroups of a free group are negligible in the graph‐based distribution, while they are exponentially generic in the word‐based distribution. Quite surprisingly, a random finite presentation generically presents the trivial group in this new distribution, while in the classical one it is known to generically present an infinite hyperbolic group. © 2012 Wiley Periodicals, Inc. Random Struct. Alg., 2013     

Homogenization of First Order Equations with (u/ε)-Periodic Hamiltonians Part II: Application to Dislocations Dynamics

This paper is concerned with a result of homogenization of a non-local first order Hamilton–Jacobi equation describing the dislocations dynamics. Our model for the interaction between dislocations involves both an integro-differential operator and a (local) Hamiltonian depending periodicly on u/ε. The first two authors studied in a previous work homogenization problems involving such local Hamiltonians. Two main ideas of this previous work are used: on the one hand, we prove an ergodicity property of this equation by constructing approximate correctors which are necessarily non periodic in space in general; on the other hand, the proof of the convergence of the solution uses here a twisted perturbed test function for a higher dimensional problem. The limit equation is a nonlinear diffusion equation involving a first order Lévy operator; the nonlinearity keeps memory of the short range interaction, while the Lévy operator keeps memory of long ones. The homogenized equation is a kind of effective plastic law for densities of dislocations moving in a single slip plane.     

de Haas-van Alphen oscillations in the underdoped high-temperature superconductor YBa2Cu3O6.5

The de Haas-van Alphen effect was observed in the underdoped cuprate YBa2Cu3O6.5 via a torque technique in pulsed magnetic fields up to 59 T. Above a field of approximately 30 T the magnetization exhibits clear quantum oscillations with a single frequency of 540 T and a cyclotron mass of 1.76 times the free electron mass, in excellent agreement with previously observed Shubnikov-de Haas oscillations. The oscillations obey the standard Lifshitz-Kosevich formula of Fermi-liquid theory. This thermodynamic observation of quantum oscillations confirms the existence of a well-defined, closed, and coherent, Fermi surface in the pseudogap phase of cuprates.