Arbres minimaux d'un graphe preordonne

We study the minimal spanning trees of a connected graph G = (X,U) where U is partially preordered (or quasi-ordered). We characterize several kinds of optimal spanning trees and give conditions for existence of strongly optimal trees. Generalizations to bases of matroids (binary matroïds in part 2) are immediate. Sone of our results are given in terms of Krugdahl's dependence graphs. They imply previous results of Rosenstiehl and Gale in the case of linear orders or preorders.     

Rational Design of Poly(2,7‐Carbazole) Derivatives for Photovoltaic Applications

A reliable model that can be used to estimate the electronic properties (i.e., the HOMO, LUMO, and band gap energies) of conjugated polymers would be a great tool for applications in organic electronics such as light‐emitting diodes, field‐effect transistors, and photovoltaic cells. Recently, poly(2,7‐carbazole) derivatives have shown promising results when used as an active donor layer in bulk heterojunction photovoltaic cells with power conversion efficiency exceeding 7%. By using a simple correlation between density functional theory (DFT) theoretical calculations performed on six model compounds (using the repeating unit) and experimental data from the six corresponding polymers, an accurate estimation of the HOMO energy level, the LUMO energy levels, and the band gap of several poly(2,7‐carbazole) derivatives was obtained. According to the theoretical data obtained for more than one hundred repeating units, fourteen new copolymers that can be used as p‐type materials in bulk heterojunction solar cells were selected and synthesized. Experimental data obtained from these materials were then used to refine the correlation between DFT and experimental data of poly(2,7‐carbazole) derivatives.

     

Cluster algebras in algebraic lie theory

We survey some recent constructions of cluster algebra structures on coordinate rings of unipotent subgroups and unipotent cells of Kac–Moody groups. We also review a quantized version of these results.     

Progress in Understanding Low‐Temperature Organic Compound Oxidation Using a Jet‐Stirred Reactor

The jet‐stirred reactor (JSR) has become a tool frequently used to study the oxidation of a wide range of reactants and particularly to obtain data for testing detailed kinetic models. This paper aims to discuss recent knowledge pertaining to low‐temperature oxidation of hydrocarbons and oxygenated reactants that has been gained from using a JSR in connection with gas chromatography, especially for the detailed quantification of cyclic ethers. Furthermore, JSR in conjunction with mass spectrometry has been applied to the detection of hydroperoxides, including ketohydroperoxides, acids, and compounds with two carbonyl functions. Finally, along with optical diagnostics, JSR has notably been used for the detection of hydrogen peroxide and OH and HO₂ radicals. These aspects are also discussed here.     

Clustering Six Electrons within “Dawson-Like” Polyoxometalate: An Open Route toward Its Post-functionalization

Super-reduction of polyoxometalates (POMs) in solution is of fundamental interest for designing innovative energy storage systems. In this article, we show that the “Dawson-like” POM can undergo a disproportionation process during its massive electron uptake, leading to species containing three metal-metal bonds as evidenced by X-ray diffraction, multi-nuclear magnetic resonance spectroscopy (¹H and ¹⁸³W NMR), extended X-ray absorption fine structure (EXAFS), UV/Vis, and voltammetry techniques. This result indicates that electron storing within metal-metal bonds is not a unique property of Keggin-type POM as postulated since the 70s. Besides, we demonstrate that the presence of an electron-rich triad in the “Dawson-like” POM allows its post-functionalization with additional tungstate ions, generating a chiral molecule that is also the largest W^IV-containing POMs known to date.     

Understanding the Reshaping of Fluorinated Polyester Vitrimers by Kinetic and DFT Studies of the Transesterification Reaction

Vitrimers are a third class of polymers gathering the mechanical properties and solvent resistance of 3D thermosets and the reprocessability of thermoplastics. This unique behaviour is due to the triggering of certain covalent exchange reactions that allow the network to rearrange upon application of a stimulus. The constitutive feature of vitrimers is the adoption of a glass-like viscosity during the rearrangement of the network, often due to an associative mechanism for the exchange reaction. Transesterification networks are one of the most studied type of vitrimers that usually require the incorporation of a catalyst, implying the associated drawbacks. Following up on a recent report on catalyst-free transesterification vitrimers in which the ester functions are particularly reactive thanks to the presence of fluorine atoms in α- or β-position, parallel DFT calculations and an experimental kinetic study on model molecules are presented in order to quantitatively assess the effect of neighbouring fluorinated groups on the transesterification reaction rate.     

Investigation of a Fluorescence Signal Amplification Mechanism Used for the Direct Molecular Detection of Nucleic Acids

A fluorescence signal amplification mechanism allowing detection limits for DNA in the zeptomolar range was investigated. Photophysical properties of the molecular system were studied in order to better explain the signal amplification that is observed. We show that the confinement of a fluorescent DNA hybridization transducer in aggregates improves its quantum yield and photostability. Furthermore, we show that the combination of the resonance energy transfer occurring within the aggregates with the use of a conjugated polymer as the hybridization transducer and donor allows ultrafast and efficient energy coupling to the aggregates and can lead to the excitation of a large number of acceptors by only one donor.     

Synthesis of New Pyridazine‐Based Monomers and Related Polymers for Photovoltaic Applications

New aromatic compounds with a pyridazine core have been synthesized. Four electron‐withdrawing monomers have been easily prepared from simple condensation reactions and ring closure procedures. Optimized HOMO, LUMO, and bandgap energy levels have been obtained. The resulting conjugated polymers have been tested in organic solar cells. First studies have revealed power conversion efficiencies up to 0.5% for an active area of 1.0 cm².

     

Supramolecular Association between γ-Cyclodextrin and Preyssler-Type Polyoxotungstate

The development of hybrid materials based on polyoxometalates constitutes a strategy for the design of multifunctional materials. The slow evaporation of an aqueous solution of [NaP₅W₃₀O₁₁₀]¹⁴⁻ in the presence of γ-Cyclodextrin (γ-CD) led to the crystallization of a K₆Na₈{[NaP₅W₃₀O₁₁₀]•(C₄₈H₈₀O₄₀)}•23H₂O (NaP₅W₃₀•1CD) supramolecular compound, which was characterized by single-crystal X-ray diffraction, IR-spectroscopy, thermogravimetric and elemental analyses. Structural analysis revealed the formation of 1:1 {[NaP₅W₃₀O₁₁₀]•[γ-CD]}¹⁴⁻ adduct in the solid state. Studies in solution by cyclic voltammetry, electrochemical impedance spectroscopy, ¹H NMR spectroscopy, and ³¹P DOSY, have demonstrated weak interactions between the inorganic anion and the macrocyclic organic molecule.     

Synthetic efforts towards the synthesis of fluorinated C-glycosidic analogues of α-galactosylceramides

An overview of the work realized by the group regarding the synthesis of fluorinated C-glycosides is described. The various strategies that were investigated allowed the synthesis of CF₂-glycosides for many carbohydrate series (glucose, mannose and galactose) and for any pseudo-anomeric center configuration (α or β). This work culminated in an efficient preparation of a synthetically useful α-CF₂-galactoside intermediate and its conversion to α-CF₂-galactoconjugates. A synthesis of α-CF₂-galactosylceramide, based on this last methodology, is currently investigated.