A new activation principle in organocatalysis is presented: halide binding through Coulombic interactions. This mode of catalysis was realized by using 3,5‐di(carbomethoxy)pyridinium ions that carry an additional electron‐withdrawing substituent on the nitrogen atom, for example, pentafluorobenzyl or cyanomethyl. For the N‐pentafluorobenzyl derivative, Coulombic interaction with the pyridinium moiety is complemented in the solid state by anion–π interactions with the perfluorophenyl ring. Bromide and chloride are bound by these cations in a 1:1 stoichiometry. Catalysis of the C? C coupling between 1‐chloroisochroman (and related electrophiles) with silyl ketene acetals occurs at ?78 °C and at low catalyst loading (2 mol %). 相似文献
ipso‐Arylative ring‐opening polymerization of 2‐bromo‐8‐aryl‐8H‐indeno[2,1‐b]thiophen‐8‐ol monomers proceeds to Mn up to 9 kg mol?1 with conversion of the monomer diarylcarbinol groups to pendent conjugated aroylphenyl side chains (2‐benzoylphenyl or 2‐(4‐hexylbenzoyl)phenyl), which influence the optical and electronic properties of the resulting polythiophenes. Poly(3‐(2‐(4‐hexylbenzoyl)phenyl)thiophene) was found to have lower frontier orbital energy levels (HOMO/LUMO=?5.9/?4.0 eV) than poly(3‐hexylthiophene) owing to the electron‐withdrawing ability of the aryl ketone side chains. The electron mobility (ca. 2×10?3 cm2 V?1 s?1) for poly(3‐(2‐(4‐hexylbenzoyl)phenyl)thiophene) was found to be significantly higher than the hole mobility (ca. 8×10?6 cm2 V?1 s?1), which suggests such polymers are candidates for n‐type organic semiconductors. Density functional theory calculations suggest that backbone distortion resulting from side‐chain steric interactions could be a key factor influencing charge mobilities. 相似文献
The concept of the coordination defect (CD) was used recently by Bevan and Martin [6] to describe the fluorite‐related superstructures of the intermediate Pr/Tb oxides. The CD is an octahedron of corner‐shared OM4/8 tetrahedra enclosing a □M4/8 tetrahedron, where □ represents an oxygen vacancy. Various linkages of CDs can define a polyhedral prism with contents appropriate to the phase composition, and this is designated the “structural motif”. The identical, parallel top and bottom planes of this prism are the “motif plane”. This concept is now extended to explore the structures of the ordered phases, delta, gamma and beta, which occur in the zirconia‐scandia system, the respective formulae being Zr3Sc4O12, Zr10Sc4O26 and Zr48Sc14O117 to Zr50Sc12O118. It is shown that the motif plane is the same in each of the known structures (delta and gamma), thus defining the close relationship between them. Possible models for the as‐yet unknown structure of the beta phase, in which this same motif plane occurs, can then be proposed. 相似文献
Hydrogels consisting of carboxylic acid groups and N‐isopropylacrylamide as pendants on their polymeric network usually exhibit volume expansion upon deprotonation or volume contraction when being heated. Demonstrated here is an anti‐intuitive case of a hydrogel containing multiple carboxylic acid groups at each crosslinking point in the polymeric network, which shrinks upon increasing pH from 1 to 7 at 37 °C or expands upon heating from 25 to 37 °C at pH 1. The unexpected volume change originates from the high percentage of the crosslinker in the polymers, as detected by solid‐state 13C NMR spectroscopy. In addition, the volume changes are thermally reversible. As the first example of the use of functional hyper‐crosslinkers to control the pH and thermal responses of nanogels, this work illustrates a new way to design soft materials with unusual behaviors. 相似文献
A new use of the thiol‐ene reaction to generate functional, redox‐tunable polymers is described. To illustrate the versatility of this approach, tailored divinyl ether monomers were polymerized with triethylene glycol dithiol to yield polymers containing either a carbonate or zwitterionic phosphocholine within the polymer backbone. Similarly, dithioerythritol was polymerized with triethylene glycol divinyl ether to yield a polymer with pendant diols and show how functional groups can be designed into either the divinyl ether or dithiol monomer. Using the thioether functional group inherent to this polymerization, all three polymers were selectively and quantitatively oxidized to either sulfoxides or sulfones by treatment with dilute hydrogen peroxide or mCPBA, respectively. With these illustrative examples, it is shown that the thiol‐ene polymerization is a broad‐reaching method to access a class of new redox‐active polymers which contain varied and dense functional‐group compositions. 相似文献
Summary: Conducting polyaniline (PANI) and montmorillonite (MMT) nanocomposites were prepared from aniline sulfate and MMT by a mechanochemical synthesis route. X‐Ray diffraction analysis confirmed that, by controlling the aniline sulfate content, mechanochemical synthesis led to two types of different formations. After polymerization, the mechanochemical route synthesized much more PANI between the clay layers compared to a solution method. The electrical conductivities of the synthesized PANI‐MMT nanocomposites in pressed pellets ranged in the order of between 10−4 and 10−3 S · cm−1.
X‐ray powder diffraction patterns of the intercalation products prepared by grinding montmorillonite with various amounts of Ani‐SO4 in a mortar. 相似文献
Several bis(triazolium)‐based receptors have been synthesized as chemosensors for anion recognition. The central naphthalene core features two aryltriazolium side‐arms. NMR experiments revealed differences between the binding modes of the two triazolium rings: one triazolium ring acts as a hydrogen‐bond donor, the other as an anion–π receptor. Receptors 92+?2BF4 ? (C6H5), 112+?2BF4 ? (4‐NO2?C6H4), and 132+?2BF4? (ferrocenyl) bind HP2O73? anions in a mixed‐binding mode that features a combination of hydrogen‐bonding and anion–π interactions and results in strong binding. On the other hand, receptor 102+?2 BF4 ? (4‐CH3O?C6H4) only displays combined Csp2?H/anion–π interactions between the two arms of the receptors and the bound anion rather than triazolium (CH)+???anion hydrogen bonding. All receptors undergo a downfield shift of the triazolium protons, as well as the inner naphthalene protons, in the presence of H2PO4? anions. That suggests that only hydrogen‐bonding interactions exist between the binding site and the bound anion, and involve a combination of cationic (triazolium) and neutral (naphthalene) C?H donor interactions. Theoretical calculations relate the electronic structure of the substituent on the aromatic group with the interaction energies and provide a minimum‐energy conformation for all the complexes that explains their measured properties. 相似文献
Just subtract water : Amphiphilic π‐conjugated acyclic oligopyrroles form solvent‐assisted H‐aggregates that give rise to vesicular structures in aqueous solution (see figure). The H‐aggregates are sensitive to the conditions and are transformed into J‐aggregates by the removal of water.
A low temperature route to crystalline titania nanostructures in thin films is presented. The synthesis is performed by the combination of sol‐gel processes, using a novel precursor for this kind of application, an ethylene glycol‐modified titanate (EGMT), and the structure templating by micro‐phase separation of a di‐block copolymer. Different temperatures around 100 °C are investigated. The nanostructure morphology is examined with scanning electron microscopy, whereas the crystal structure and thin film compositions are examined by scattering methods. Optoelectronic measurements reveal the band‐gap energies and sub‐band states of the titania films. An optimum titania thin film is created at temperatures not higher than 90 °C, regarding sponge‐like morphology with pore sizes of 25–30 nm, porosity of up to 71 % near the sample surface, and crystallinity of titania in the rutile phase. The low temperature during synthesis is of high importance for photovoltaic applications and renders the resulting titania films interesting for future energy solutions. 相似文献
The defect chemistry of the ferroelectric material PbTiO3 after doping with FeIII acceptor ions is reported. Using advanced transmission electron microscopy and powder X‐ray and neutron diffraction, we demonstrate that even at concentrations as low as circa 1.7 % (material composition approximately ABO2.95), the oxygen vacancies are trapped into extended planar defects, specifically crystallographic shear planes. We investigate the evolution of these defects upon doping and unravel their detailed atomic structure using the formalism of superspace crystallography, thus unveiling their role in nonstoichiometry in the Pb‐based perovskites. 相似文献