A highly‐ordered 3D covalent fullerene framework is presented with a structure based on octahedrally functionalized fullerene building blocks in which every fullerene is separated from the next by six functional groups and whose mesoporosity is controlled by cooperative self‐assembly with a liquid‐crystalline block copolymer. The new fullerene‐framework material was obtained in the form of supported films by spin coating the synthesis solution directly on glass or silicon substrates, followed by a heat treatment. The fullerene building blocks coassemble with a liquid‐crystalline block copolymer to produce a highly ordered covalent fullerene framework with orthorhombic Fmmm symmetry, accessible 7.5 nm pores, and high surface area, as revealed by gas adsorption, NMR spectroscopy, small‐angle X‐ray scattering (SAXS), and TEM. We also note that the 3D covalent fullerene framework exhibits a dielectric constant significantly lower than that of the nonporous precursor material. 相似文献
We propose a mechanism for defect‐assisted covalent binding of graphene to the surface of amorphous silica (a‐SiO2) based on first‐principles density functional calculations. Our calculations show that a dioxasilirane group (DOSG) on a‐SiO2 may react with graphene to form two Si? O? C linkages with a moderate activation barrier (≈0.3 eV) and considerable exothermicity (≈1.0 eV). We also examine DOSG formation via the adduction of molecular O2 to a silylene center, which is an important surface defect in a‐SiO2, and briefly discuss modifications in the electronic structure of graphene upon the DOSG‐assisted chemical binding onto the a‐SiO2 surface. 相似文献
A complementary double‐covalent functionalization of single‐wall carbon nanotubes (SWCNTs) that involves both solubilizing ionic liquids and electroactive moieties is reported. Our strategy is a simple and efficient methodology based on the stepwise functionalization of the nanotube surface with two different organic moieties. In a first instance, oxidized SWCNTs are amidated with ionic liquid precursors, and further treated with n‐butyl bromide to afford SWCNTs functionalized with 1‐butylimidazolium bromide. This approach allows tuneable polarity induced by anion exchange, which has an effect on the relative solubility of the modified SWCNTs in water. Subsequently, a 1,3‐dipolar cycloaddition reaction was performed to introduce the electron‐acceptor 11,11,12,12‐tetracyano‐9,10‐anthra‐para‐quinodimethane (TCAQ) unit on the SWCNTs. Furthermore, to evaluate the influence of the functional group position, the TCAQ electroactive molecule was anchored through an esterification reaction onto previously oxidized SWCNTs, followed by the Tour reaction to introduce the ionic liquid functions. IR and Raman spectroscopies, thermogravimetric analysis (TGA), UV/Vis/NIR spectroscopy, transmission electron microscopy (TEM), and X‐ray photoelectron spectroscopy (XPS) were employed and clearly confirmed the double‐covalent functionalization of the SWCNTs. 相似文献
We combine density functional theory calculations and scanning tunneling microscopy investigations to identify the relevant chemical species and reactions in the nucleation phase of chemical vapor deposition. tert‐Butylphosphine (TBP) was deposited on a silicon substrate under conditions typical for surface functionalization and growth of semiconductor materials. On the activated hydrogen‐covered surface H/Si(001) it forms a strong covalent P?Si bond without loss of the tert‐butyl group. Calculations show that site preference for multiple adsorption of TBP is influenced by steric repulsion of the adsorbate's bulky substituent. STM imaging furthermore revealed an anisotropic distribution of TBP with a preference for adsorption perpendicular to the surface dimer rows. The adsorption patterns found can be understood by a mechanism invoking stabilization of surface hydrogen vacancies through electron donation by an adsorbate. The now improved understanding of nucleation in thin‐film growth may help to optimize molecular precursors and experimental conditions and will ultimately lead to higher quality materials. 相似文献
A highly efficient and reusable molybdenum‐based catalyst has been synthesized by covalent grafting of a bis(phenol) diamine ligand, namely 2‐(((2‐bromoethyl)(2‐((3,5‐di‐tert‐butyl‐2‐hydroxybenzyl)amino)ethyl)amino)methyl)‐4,6‐di‐tert‐butylphenol, onto functionalized ordered mesoporous silica (SBA‐15) followed by complexation with MoO2(acac)2. The resulting organic–inorganic hybrid material was found to be a highly effective catalyst for oxygenation of various sulfides to their corresponding sulfoxides or sulfones. The catalyst was characterized using transmission and scanning electron microscopies, X‐ray photoelectron, Fourier transform infrared and atomic absorption spectroscopies, Brunauer–Emmett–Teller surface area analysis and thermogravimetric analysis. Mild reaction conditions, high selectivity and easy recovery and reusability of the catalyst render the presented protocol very useful for addressing industrial needs and environmental concerns. 相似文献
Featuring the simultaneous generation of a library of compounds from a certain intermediate, divergent synthesis has found increasing applications in the construction of natural products and potential medicines. Inspired by this approach, presented herein is a general strategy to introduce functionality, in a divergent manner, into covalent organic frameworks (COFs). This modular protocol includes two stages of covalent assembly, through which functional COFs can be constructed by a three‐step transformation of a key platform molecule, such as 4,7‐dibromo‐2‐chloro‐1H‐benzo[d]imidazole (DBCBI). Constructed herein are four types of chiral COFs (CCOFs) from DBCBI by nucleophilic substitution, Suzuki coupling, and imine formation. The unique array of eight isoframework CCOFs allowed investigation of their catalytic performance and structure–activity relationship in an asymmetric amination reaction. 相似文献
The on‐surface polymerization of 1,3,6,8‐tetrabromopyrene (Br4Py) on Cu(111) and Au(111) surfaces under ultrahigh vacuum conditions was investigated by a combination of scanning tunneling microscopy (STM), X‐ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. Deposition of Br4Py on Cu(111) held at 300 K resulted in a spontaneous debromination reaction, generating the formation of a branched coordination polymer network stabilized by C?Cu?C bonds. After annealing at 473 K, the C?Cu?C bonds were converted to covalent C?C bonds, leading to the formation of a covalently linked molecular network of short oligomers. In contrast, highly ordered self‐assembled two‐dimensional (2D) patterns stabilized by both Br?Br halogen and Br?H hydrogen bonds were observed upon deposition of Br4Py on Au(111) held at 300 K. Subsequent annealing of the sample at 473 K led to a dissociation of the C?Br bonds and the formation of disordered metal‐coordinated molecular networks. Further annealing at 573 K resulted in the formation of covalently linked disordered networks. Importantly, we found that the chosen substrate not only plays an important role as catalyst for the Ullmann reaction, but also influences the formation of different types of intermolecular bonds and thus, determines the final polymer network morphology. DFT calculations further support our experimental findings obtained by STM and XPS and add complementary information on the reaction pathway of Br4Py on the different substrates. 相似文献
Structured and functional materials are of the utmost importance for the development of microelectronic technology. We report on a method to obtain a highly ordered organic molecular layer on a mineral substrate. We took advantage of the regular array of reactive sites present at the single-crystal surface of topaz to perform a liquid-phase silanization reaction. The grazing-incidence diffraction technique was used to characterize the bare and covalently coated surfaces. The ordering of the monomolecular organic layer reproduces the perfect single-crystal structure of the cleaved surface over millimeter distances. 相似文献
A novel biodegradable thiazolidine‐2‐thione functional chain transfer agent was synthesized and employed as a reversible additional fragmentation chain transfer agent to prepare well‐defined semitelechelic poly‐N‐(2‐hydroxypropyl) methacrylamides (polyHPMAs) with predetermined molecular weights and narrow polydispersities. The protein reactive group, thiazolidine‐2‐thione, was located at the polymer chain ends fixed by biodegradable disulfide bonds. The functional polyHPMA chains were subsequently conjugated to protein (lysozyme) by exploiting reactions between the thiazolidine‐2‐thione functionality and amine residues on the protein surface to form covalent amide linkages. The in vitro bioactivities of the lysozyme–polyHPMA conjugates were assessed by using Micrococcus lysodeikticus cells as substrates. The lysozyme bioactivity was significantly reduced following the conjugation procedure. However, cleavage of the polymer chains from the bioconjugates (under reducing conditions) yielded free protein and a remarkable recovery of bioactivity. In vivo tests were performed by subcutaneous injection into mice and clearly demonstrated decreased proteolytic degradation for the protein–polymer conjugate when compared with native protein, indicating effective protein protection through a conjugation strategy. This bioreversible approach to conjugation allows for a balance to be made between protein protection and effective bioactivity maintenance. 相似文献
Summary: Binary symmetric diblock copolymer blends, that is, low‐molecular‐weight poly(styrene‐block‐methyl methacrylate) (PS‐b‐PMMA) and high‐molecular‐weight poly(styrene‐block‐methacrylate) (PS‐b‐PMA), self‐assemble on silicon substrates to form structures with highly ordered nanoholes in thin films. As a result of the chemically similar structure of the PMA and the PMMA block, the PMMA chain penetrates through the large PMA block that absorbs preferentially on the polar silicon substrate. This results in the formation of nanoholes in the PS continuous matrix.
An atomic force microscopy image of the thin film obtained from the blend of low‐molecular‐weight PS‐b‐PMMA and high‐molecular‐weight PS‐b‐PMA. The regular array of nanoholes in the films surface is clearly visible. 相似文献
Poor control on the exfoliation of covalent organic frameworks (COFs) remains a disadvantage for their application as two‐dimensional nanosheets. An equally important problem is the reversible control at the available surface charges on COFs. Herein, a strategy for the reversible exfoliation, re‐stacking, and surface‐charge control of a propidium iodide based ionic covalent organic framework, PI‐TFP , using cucurbit[7]uril (CB[7]) induced molecular recognition, is reported. The surface charge on PI‐TFP facilitates its initial self‐exfoliation. However, complexation with CB[7] resulted in re‐stacking with concomitant decrease in zeta potential from +28±3.0 to +0.004±0.003 mV. Addition of 1‐adamantylamine hydrochloride (AD) facilitates decomplexation of PI‐TFP from CB[7], resulting in exfoliation and an increase in zeta potential to +24±3.0 mV. Such control on the exfoliation, re‐stacking, and the associated regulation of the surface charge in PI‐TFP was exploited for controlling bacterial growth. Thus, the activity of E. coli and S. aureus bacteria obtained with the self‐exfoliated PI‐TFP could be reversibly controlled by the CB[7]/AD pair. 相似文献
A domino approach consisting of up to five consecutive steps to access either highly substituted dispiranes or π‐helicenes from oligoyne chains is reported. The domino sequence consists of several carbopalladation reactions, a Stille cross‐coupling to obtain the helicenes, and, depending on the steric demands of the helicene, a final 6π‐electrocyclization to afford the dispiranes. Formally, the latter transformation contravenes the Woodward–Hoffmann rules, as revealed by X‐ray crystallography of the dispirane. Additionally, the racemization barrier of the (Z,Z,Z)‐triene‐based helicene has been determined by a kinetic analysis and compared with results from density functional theory calculations. Characteristic points on the reaction coordinate were further analyzed according to their relaxed force constants (compliance constants). 相似文献
The development of fluorescent probes to image forces in cells is an important challenge in chemistry and biology. Planarizable push‐pull probes have been introduced recently for this purpose. To provide most valuable information on forces in complex systems, these mechanosensitive ‘flipper’ probes will have to be localized by molecular recognition of targets of interest. Here we report fluorescent flippers that selectively recognize gangliosides on the surface of lipid bilayer membranes by formation of dynamic covalent boronate esters. The original flipper probes were equipped with 2‐fluorophenyl boronic acids and benzoboroxoles using consecutive triazole and oxime ligation. Evaluation was done in large unilamellar vesicles composed of EYPC/SM/CL/GM 40:40‐x:20:x to obtain mixed membranes with separate liquid‐disordered (Ld) and ganglioside (GM) containing liquid‐ordered (Lo) domains. With increasing GM concentration, fluorescence intensities increased and excitation maximum shifted to the red. Deconvolution of the spectra confirmed that these changes originate from a migration of the flipper probes from Ld to Lo domains upon binding to the gangliosides and thus the planarization in the more ordered environment. Control mechanophores without boronic acids failed to show the same response, and fructose partially inhibited the ganglioside sensitivity. These results demonstrate that it is possible to selectively accumulate mechanosensitive flipper probes in Lo domains and, more generally, that probe localization in complex membranes is possible and matters. 相似文献
Modelling of the two‐dimensional polymerization of 1,4‐benzene diboronic acid molecules on the Ag(111) surface, which leads to the formation of a covalent organic framework, is reported. An estimation of free enthalpy is given that takes into account the constraints induced by the molecular adsorption on the surface. The various thermodynamic functions, enthalpies, entropies, and free enthalpies, are obtained from DFT calculations. The entropic effect of the surface plays an important role in the polymerization free energy. A germination threshold is obtained.相似文献
On-surface synthesis is emerging as a highly rational bottom-up methodology for the synthesis of molecular structures that are unattainable or complex to obtain by wet chemistry. Here, oligomers of meta-polyaniline, a known ferromagnetic polymer, were synthesized from para-aminophenol building-blocks via an unexpected and highly specific on-surface formal 1,4 Michael-type addition at the meta position, driven by the reduction of the aminophenol molecule. We rationalize this dehydrogenation and coupling reaction mechanism with a combination of in situ scanning tunneling and non-contact atomic force microscopies, high-resolution synchrotron-based X-ray photoemission spectroscopy and first-principles calculations. This study demonstrates the capability of surfaces to selectively modify local molecular conditions to redirect well-established synthetic routes, such as Michael coupling, towards the rational synthesis of new covalent nanostructures. 相似文献