Vinylene-Linked Covalent Organic Frameworks by Base-Catalyzed Aldol Condensation

Two 2D covalent organic frameworks (COFs) linked by vinylene (−CH=CH−) groups (V‐COF‐1 and V‐COF‐2) are synthesized by exploiting the electron deficient nature of the aromatic s‐triazine unit of C3‐symmetric 2,4,6‐trimethyl‐s‐triazine (TMT). The acidic terminal methyl hydrogens of TMT can easily be abstracted by a base, resulting in a stabilized carbanion, which further undergoes aldol condensation with multitopic aryl aldehydes to be reticulated into extended crystalline frameworks (V‐COFs). Both V‐COF‐1 (with terepthalaldehyde (TA)) and V‐COF‐2 (with 1,3,5‐tris(p‐formylphenyl)benzene (TFPB)) are polycrystalline and exhibit permanent porosity and BET surface areas of 1341 m2 g−1 and 627 m2 g−1, respectively. Owing to the close proximity (3.52 Å) of the pre‐organized vinylene linkages within adjacent 2D layers stacked in eclipsed fashion, [2+2] photo‐cycloadditon in V‐COF‐1 formed covalent crosslinks between the COF layers.TU Berlin, Open-Access-Mittel - 2019DFG, 390540038, EXC 2008: UniSysCa

Preparation of multi-allylic dendronized polymers via atom-transfer radical polymerization

International audienceAtom-transfer radical polymerization (ATRP) was investigated to polymerize a styrene monomer carrying carbosilane dendrons with 6 terminal allyl branches. Polymers with a monomodal molar mass distribution and low polydispersity have been produced, while by comparison the free-radical polymerization technique led to chain transfer early in the polymerization. Steric effect brought by the dendrons result in a slow polymerization rate, leading to an apparent saturation of the degree of polymerization. By pushing up the polymerization conditions (eg. increase of temperature or concentration), interchain couplings started to take place, most likely from reactions at the allyl branches. These results are very similar to the ones previously reported for the anionic polymerization of this same multi-allylic dendronized monomer. § present addresses: P.O. Schwartz, Alsachim SAS

Programmable Photocatalytic Activity of Multicomponent Covalent Organic Frameworks Used as Metallaphotocatalysts

The multicomponent approach allows to incorporate several functionalities into a single covalent organic framework (COF) and consequently allows the construction of bifunctional materials for cooperative catalysis. The well-defined structure of such multicomponent COFs is furthermore ideally suited for structure-activity relationship studies. We report a series of multicomponent COFs that contain acridine- and 2,2’-bipyridine linkers connected through 1,3,5-benzenetrialdehyde derivatives. The acridine motif is responsible for broad light absorption, while the bipyridine unit enables complexation of nickel catalysts. These features enable the usage of the framework materials as catalysts for light-mediated carbon−heteroatom cross-couplings. Variation of the node units shows that the catalytic activity correlates to the keto-enamine tautomer isomerism. This allows switching between high charge-carrier mobility and persistent, localized charge-separated species depending on the nodes, a tool to tailor the materials for specific reactions. Moreover, nickel-loaded COFs are recyclable and catalyze cross-couplings even using red light irradiation

Constitutional isomerism of the linkages in donor–acceptor covalent organic frameworks and its impact on photocatalysis

結合様式の制御により高効率な水素発生反応を実現 --有機二次元高分子光触媒の創出に新たな戦略を--. 京都大学プレスリリース. 2022-12-13.When new covalent organic frameworks (COFs) are designed, the main efforts are typically focused on selecting specific building blocks with certain geometries and properties to control the structure and function of the final COFs. The nature of the linkage (imine, boroxine, vinyl, etc.) between these building blocks naturally also defines their properties. However, besides the linkage type, the orientation, i.e., the constitutional isomerism of these linkages, has rarely been considered so far as an essential aspect. In this work, three pairs of constitutionally isomeric imine-linked donor-acceptor (D-A) COFs are synthesized, which are different in the orientation of the imine bonds (D-C=N-A (DCNA) and D-N=C-A (DNCA)). The constitutional isomers show substantial differences in their photophysical properties and consequently in their photocatalytic performance. Indeed, all DCNA COFs show enhanced photocatalytic H2 evolution performance than the corresponding DNCA COFs. Besides the imine COFs shown here, it can be concluded that the proposed concept of constitutional isomerism of linkages in COFs is quite universal and should be considered when designing and tuning the properties of COFs

附属図書館における電算化(I)

Ce travail de thèse porte sur la synthèse de polymères dendronisés fonctionnels porteurs de courtes chaînes oxyéthylènes. Leur préparation est effectuée en deux étapes : la polymérisation anionique vivante de macromonomères dendritiques à chaînes terminales allyles (i.e. des styrènes porteurs de 2 ou 3 dendrons carbosilane de 1ère génération), suivie du greffage des chaînes oxyéthylènes via une addition radicalaire de thiol. Des taux de fonctionnalisation quasi-quantitatifs ont été obtenus, permettant d’incorporer jusqu’à 6 ou 9 chaînes oxyéthylènes par unité répétitive. L’étude des propriétés d’extraction et de complexation montre une remarquable sélectivité pour l’ion argent, avec une association privilégiée d’un cation par dendron. Par ailleurs, selon le degré d’hydrophilie, contrôlé par la densité des motifs oxyéthylènes greffés, la solubilité des polymères en milieu aqueux peut être ajustée jusqu’à l’apparition d’un comportement inverse de solubilité en fonction de la température.The aim of this work consists in the synthesis of surface-functionalized dendronized polymers with oxyethylene chains of short length. These materials are prepared in two steps, by living anionic polymerization of macromonomers with allyl terminal chains (i.e. styrene bearing 2 or 3 carbosilane dendrons of first generation), followed by a functionalization step with oxyethylene chains via a radical addition of thiol. Almost quantitative functionalization could be achieved, yielding polymers with up to 6 or 9 oxyethylene chains per repeat unit. The extraction and complexation studies show a remarkable selectivity toward silver cation, with a preferred association of one cation per dendron. According to the degree of hydrophilicity, as controlled by the density of the grafted oxyethylene chains, it is possible to adjust the solubility of the polymers in water up to the appearance of a lower critical solution temperature (LCST)

Synthèse de polymères dendronisés pour la reconnaissance ionique et à propriétés thermosensibles

The aim of this work consists in the synthesis of surface-functionalized dendronized polymers with oxyethylene chains of short length. These materials are prepared in two steps, by living anionic polymerization of macromonomers with allyl terminal chains (i.e. styrene bearing 2 or 3 carbosilane dendrons of first generation), followed by a functionalization step with oxyethylene chains via a radical addition of thiol. Almost quantitative functionalization could be achieved, yielding polymers with up to 6 or 9 oxyethylene chains per repeat unit. The extraction and complexation studies show a remarkable selectivity toward silver cation, with a preferred association of one cation per dendron. According to the degree of hydrophilicity, as controlled by the density of the grafted oxyethylene chains, it is possible to adjust the solubility of the polymers in water up to the appearance of a lower critical solution temperature (LCST).Ce travail de thèse porte sur la synthèse de polymères dendronisés fonctionnels porteurs de courtes chaînes oxyéthylènes. Leur préparation est effectuée en deux étapes : la polymérisation anionique vivante de macromonomères dendritiques à chaînes terminales allyles (i.e. des styrènes porteurs de 2 ou 3 dendrons carbosilane de 1ère génération), suivie du greffage des chaînes oxyéthylènes via une addition radicalaire de thiol. Des taux de fonctionnalisation quasi-quantitatifs ont été obtenus, permettant d incorporer jusqu à 6 ou 9 chaînes oxyéthylènes par unité répétitive. L étude des propriétés d extraction et de complexation montre une remarquable sélectivité pour l ion argent, avec une association privilégiée d un cation par dendron. Par ailleurs, selon le degré d hydrophilie, contrôlé par la densité des motifs oxyéthylènes greffés, la solubilité des polymères en milieu aqueux peut être ajustée jusqu à l apparition d un comportement inverse de solubilité en fonction de la température.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Imidazolium functionalized SBA-15 type silica: efficient organocatalysts for Henry and cycloaddition reactions

International audienceWe report the synthesis of mesoporous SBA-15 type silica bearing ionic imidazolium substructures. Surface functionalization was achieved via post-synthesis grafting reactions using bis-silylated imidazolium precursors onto a mesoporous SBA-15 type silica support. The grafting reactions were monitored via solid state NMR spectroscopy, nitrogen sorption, transmission electron microscopy and thermogravimetry. Post synthesis grafting is the most convenient way to achieve highly stable functionalized solids displaying excellent accessibility of the immobilized functional groups combined with high chemical stability. The solids obtained via post synthesis grafting reactions appeared as highly efficient and reusable heterogeneous organocatalysts for Henry reactions and the cycloadditions of CO2 to epichlorohydrin

Dendronized Polymers with Peripheral Oligo(ethylene oxide) Chains: Thermoresponsive Behavior and Shape Anisotropy in Solution

International audienc

Delayed Western Gotland Basin (Baltic Sea) ventilation in response to the onset of a Mid-Holocene climate oscillation

The marine-terrestrial Baltic ecosystem is sensitive to a range of environmental forcing and thresholds. Multi-archive investigations of its evolution require a precise synchronization of the considered archives. Here, we apply globally common cosmogenic radionuclide production rate variations to synchronize 10Be records from brackish Western Gotland Basin (Baltic Sea) and terrestrial lake Tiefer See (NE Germany) sediments to the atmospheric 14C time-scale and investigate phase-relationships in proxy responses in the southern Baltic realm associated with the onset of a centennial Mid-Holocene climate oscillation ∼5800 a BP. Based on paired molybdenum and titanium records, we identify a 98 ± 81-year delay in Western Gotland Basin ventilation, compared to the terrestrial response at the onset of the recorded Mid-Holocene climate oscillation. Most plausible mechanism for this delay is strengthened stratification in response to enhanced freshwater input during the first decades of the oscillation