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1.
Significant anisotropic electrical conduction in organosilica films is achieved by long‐range orientation of electroactive perylene bisimide (PBI) moieties in the silica scaffold. A new PBI‐based organosilane precursor is designed with lyotropic liquid‐crystalline properties. The PBI precursor with triethoxysilylphenyl groups exhibits a hexagonal columnar phase in the presence of organic solvents. The lyotropic liquid‐crystalline behavior of the precursor enables the preparation of dip‐coated films consisting of uniaxially aligned columnar aggregates of the PBI precursor on the centimeter scale. The oriented structure is successfully fixed by in situ polycondensation, which yields insoluble, thermally stable PBI–silica hybrid films. The oriented organosilica films doped with hydrazine exhibit high electrical conductivities on the order of 10?2 S cm?1, which are at the highest level for organosilica materials, and are comparable to those of all‐organic PBI assemblies. Definite anisotropy of conductivities is also found for these films. The present results suggest that the induction of significant electrical properties in organic molecular assemblies is compatible with the structural stabilization by inorganic–organic hybridization.  相似文献   

2.
The self‐assembly and polycondensation of a triphenylamine‐derived organosilane precursor in an aqueous mixture result in electroactive organosilica nanotubes without the use of template materials. The nanotubes are easily synthesized by the slow addition of water to an acidified organic solution of the precursor, followed by basification with an aqueous NaOH solution. In contrast to conventional sol–gel methods that yield amorphous organosilica materials, the present organosilica nanotubes exhibit birefringence due to the orientation of the triphenylamine moieties within the tube walls. The template‐free formation of nanotubes with optical anisotropy suggests a roll‐up mechanism of 2D nanosheets consisting of hydrolyzed precursors. The organosilica nanotubes contain a high density of oriented triphenylamine moieties, and exhibit a mixed‐valence state with a near‐infrared absorption band due to chemical doping along with high electrical conductivities, on the order of 10−3–10−2 S cm−1. Such nanostructured organosilicas, comprising an electroactive framework, are useful for optoelectronic and photocatalytic applications.  相似文献   

3.
Mesostructured forms of silica (denoted MSU‐J) and aminopropyl‐functionalized silica (denoted AP‐MSU‐J) with wormhole framework structures are effective reinforcing agents for a rubbery epoxy polymer. At loadings of 2.0–10 wt %, MSU‐J silica with an average framework pore size of 14 nm (65 °C assembly temperature) provides superior reinforcement properties in comparison to MSU‐J silica with a smaller average framework pore size of 5.3 nm (25 °C assembly temperature), even though the surface area of the larger pore mesostructure (670 m2 g?1) is substantially lower than the smaller pore mesostructure (964 m2 g?1). The introduction of 5.0 and 10 mol % aminopropyl groups in the wormhole framework walls decreases the textural properties in comparison to the pure silica analogs. AP‐MSU‐J organosilicas increase the tensile strength as well as the strain‐at‐break of the rubbery epoxy mesocomposites in comparison to MSU‐J silica as a reinforcing agent. The improved toughness provided by the aminopropyl functionalized mesostructures is attributable in part to covalent bond formation between the mesostructured silica walls and the cured epoxy matrix and to a more ductile mesostructure framework in comparison to a pure silica framework. An organosilica derivative containing 20 mol % aminopropyl groups, but lacking a mesostructured framework, provides little or no improvement in polymer tensile properties, demonstrating that an ordered porous network is essential for polymer reinforcement. In general, the reinforcement benefits provided by mesostructures with larger framework pores are superior to those provided by smaller pore derivatives, most likely because of more efficient polymer impregnation of the particle mesopores. The presence of a mesostructured form of the organosilica is essential for improving the mechanical properties of the epoxy polymer.  相似文献   

4.
Periodic mesoporous organosilica nanoparticles emerge as promising vectors for nanomedicine applications. Their properties are very different from those of well‐known mesoporous silica nanoparticles as there is no silica source for their synthesis. So far, they have only been synthesized from small bis‐silylated organic precursors. However, no studies employing large stimuli‐responsive precursors have been reported on such hybrid systems yet. Here, the synthesis of porphyrin‐based organosilica nanoparticles from a large octasilylated metalated porphyrin precursor is described for applications in near‐infrared two‐photon‐triggered spatiotemporal theranostics. The nanoparticles display unique interconnected large cavities of 10–80 nm. The framework of the nanoparticles is constituted with J‐aggregates of porphyrins, which endows them with two‐photon sensitivity. The nanoparticle efficiency for intracellular tracking is first demonstrated by the in vitro near‐infrared imaging of breast cancer cells. After functionalization of the nanoparticles with aminopropyltriethoxysilane, two‐photon‐excited photodynamic therapy in zebrafish is successfully achieved. Two‐photon photochemical internalization in cancer cells of the nanoparticles loaded with siRNA is also performed for the first time. Furthermore, siRNA targeting green fluorescent protein complexed with the nanoparticles is delivered in vivo in zebrafish embryos, which demonstrates the versatility of the nanovectors for biomedical applications.  相似文献   

5.
Although defects are traditionally perceived as undesired feature, the prevalence of tenacious low‐coordinated defects can instead give rise to desirable functionalities. Here, a spontaneous etching of mesostructured crystal, cyanide‐bridged cobalt‐iron (CN‐CoFe) organometallic hybrid into atomically crafted open framework that is populated with erosion‐tolerant high surface energy defects is presented. Unprecedently, the distinct mechanistic etching pathway dictated by the mesostructured assembly, bulk defects, and strong intercoordinated cyanide‐bridged hybrid mediates not only formation of excess low‐coordinated defects but also more importantly stabilizes them against prevailing dissolution and migration issues. Clearly, the heteropolynuclear cyanide bonded inorganic mesostructured clusters sanction the restructuring of a new breed of stable organometallic polymorph with 3D accessible structure enclosed by electrochemical active atomic stepped edges and high index facets. The exceptional electrocatalysis performance supports the assertion that defective mesostructured polymorph offers a new material paradigm to synthetically tailor the elementary building block constituents toward functional materials.  相似文献   

6.
A new and highly reproducible method to obtain mesostructured titania materials is introduced in this contribution. The mesostructured titania is obtained by employing self‐assembled structures of non‐ionic alkyl‐poly(ethylene oxide) surfactants as templates. The materials are produced without additional solvents such as alcohols, or even water. Only the titanium(IV ) ethoxide and the surfactant (C12EO10) are needed. Water, in the form of that attached to the surfactant and from the atmosphere, induces growth of titania nanoclusters in the synthesis sol. It is indicated that these nanoclusters interact with the surfactant EO‐head groups to form a new titanotropic amphiphile. The new amphiphiles self‐assemble into titanium nanocluster–surfactant hybrid lyotropic phases, which are transformed to the final mesostructured materials by further condensation of the titania network. The titania materials can be obtained also with noble‐metal particles immobilized in the mesostructured framework. It is seen that when different metal salts are used as the metal precursors, different interactions with the titania walls are found. The materials are characterized by X‐ray diffraction (XRD), polarization optical microscopy (POM), transmission electron microscopy (TEM), UV‐vis spectroscopy, and micro‐Raman analysis.  相似文献   

7.
This contribution describes the preparation of multifunctional yolk–shell nanoparticles (YSNs) consisting of a core of silica spheres and an outer shell based on periodic mesoporous organosilica (PMO) with perpendicularly aligned mesoporous channels. The new yolk–shell hybrid materials were synthesised through a dual mesophase and vesicle soft templating method. The mesostructure of the shell, the dimension of the hollow space (4~52 nm), and the shell thickness (16~34 nm) could be adjusted by precise tuning of the synthesis parameters, as evidenced by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen sorption investigations. Various metal nanoparticles (e.g., Au, Pt, and Pd) were encapsulated and confined in the void space between the core and the shell using impregnation and reduction of adequate metal precursors. The selective oxidation of various alcohol substrates was then carried out to illustrate the benefits of such an architecture in catalysis. High conversion (~100%) and excellent selectivity (~99%) were obtained over Pd nanoparticles encapsulated in the hybrid PMO yolk–shell structures.  相似文献   

8.
Mesostructured silica thin films and particles prepared by surfactant‐templated sol–gel techniques are highly versatile substrates for the formation of functional materials. The ability to deliberately place molecules possessing desired activities in specific spatially separated regions of the nanostructure is an important feature of these materials. Such placement utilizes strategies that exploit the physical and chemical differences between the silica framework and the templated pores. As an example of placement of pairs of molecules, donor and acceptor molecules can be targeted to different regions of mesostructured thin films and energy transfer between them can be measured. The results not only demonstrate the spatial separation but also are used as a molecular ruler to measure the average distance between them. Mesostructured silica is also an excellent support for molecular machines. Molecules that undergo large amplitude motion, when attached to the silica, can function as impellers and nanovalves when activated by light, electrical (redox) and chemical (pH, competitive binding) energy. Derivatized azobenzene molecules, attached to pore walls by using one of the placement strategies, function as impellers that can move other molecules through the pores. Rotaxanes and pseudorotaxanes, placed at pore entrances, function as gatekeepers that can trap and release molecules from the pores when stimulated. Deliberately placed functional molecules on and in mesostructured silica offer many possibilities for both fundamental studies on the nanoscale and for applications in fields as diverse as fluidics, biological drug delivery and controlled release.  相似文献   

9.
Lanthanide‐doped luminescent nanoparticles are an appealing system for nanothermometry with biomedical applications due to their sensitivity, reliability, and minimal invasive thermal sensing properties. Here, four unique hybrid organic–inorganic materials prepared by combining β‐NaGdF4 and PMOs (periodic mesoporous organosilica) or mSiO2 (mesoporous silica) are proposed. PMO/mSiO2 materials are excellent candidates for biological/biomedical applications as they show high biocompatibility with the human body. On the other hand, the β‐NaGdF4 matrix is an excellent host for doping lanthanide ions, even at very low concentrations with yet very efficient luminescence properties. A new type of Er3+–Yb3+ upconversion luminescence nanothermometers operating both in the visible and near infrared regime is proposed. Both spectral ranges permit promising thermometry performance even in aqueous environment. It is additionally confirmed that these hybrid materials are non‐toxic to cells, which makes them very promising candidates for real biomedical thermometry applications. In several of these materials, the presence of additional voids leaves space for future theranostic or combined thermometry and drug delivery applications in the hybrid nanostructures.  相似文献   

10.
Functionalized metal–organic frameworks (fu‐MOFs) of general formula [Zn2(fu‐L)2dabco]n show unprecedentedly large uniaxial positive and negative thermal expansion (fu‐L = alkoxy functionalized 1,4‐benzenedicarboxylate, dabco = 1,4‐diazabicyclo[2.2.2]octane). The magnitude of the volumetric thermal expansion is more comparable to property of liquid water rather than any crystalline solid‐state material. The alkoxy side chains of fu‐L are connected to the framework skeleton but nevertheless exhibit large conformational flexibility. Thermally induced motion of these side chains induces extremely large anisotropic framework expansion and eventually triggers reversible solid state phase transitions to drastically expanded structures. The thermo‐responsive properties of these hybrid solid–liquid materials are precisely controlled by the choice and combination of fu‐Ls and depend on functional moieties and chain lengths. In principle, this combinatorial approach allows for a targeted design of extreme thermo‐mechanical properties of MOFs addressing the regime between crystalline solid matter and the liquid state.  相似文献   

11.
Tetraphenylpyrene has been selected as a discotic core to promote liquid‐crystalline fluorescent columns in view of its high fluorescence quantum yield in solution and ease of substitution by flexible lateral side chains. The synthesis and characterization of ten new derivatives of pyrene have been carried out; the pyrene core has been substituted at the 1,3,6,8‐positions by phenylene rings bearing alkoxy, ester, thioether, or tris(alkoxy)benzoate groups on the para position; the compounds have been characterized by mass spectrometry and 1H NMR and UV‐vis spectroscopies. In order to generate liquid‐crystalline phases, the nature, number, and size of the side chains as well as the degree of polarity around the tetraphenylpyrene core have been varied. However, the desired liquid‐crystalline behavior has not been observed. The supramolecular order together with the absorption and emission properties in solution and the solid state are discussed and compared to theoretical predictions. Quantum‐chemical calculations rationalize the high solid‐state fluorescence of a tetraphenylpyrene derivative for which the crystal structure has been determined.  相似文献   

12.
Novel oxygen sensors consisting of a [Ru(bpy)2phen]2+ (bpy: 2,2′‐bipyridyl, phen: phenathroline) portion covalently grafted to a mesostructured silica‐based network are prepared in situ via a sol–gel approach with the help of cetyltrimethylammoniumbromide (CTAB) surfactant. 1,10‐Phenanthroline covalently grafted to 3‐(triethoxysilyl)propyl isocyanate is used as not only the sol–gel precursor but also as the second ligand of the Ru(bpy)2Cl2 · 2H2O complex to prepare the sol–gel‐derived mesostructured silicates for an oxygen sensor. For comparison purposes, the oxygen sensors in which [Ru(bpy)2phen]Cl2 is conventionally physically incorporated into the matrix are also prepared. Elemental analysis, NMR, Fourier transform IR, UV‐vis electronic absorption, luminescence‐intensity quenching Stern–Volmer plots, and excited‐state decay analysis are used to characterize the obtained oxygen sensors. These obtained bulk xerogels and spin‐coated thin films show that the homogeneity and the sensitivity of the covalently grafted samples are superior to those of the physically incorporated ones, and the highest sensitivity is obtained in the mesostructured bulk xerogel. This improvement in oxygen sensitivity is attributed to the increased diffusivity of oxygen in the uniform and nearly parallel porous structure of the Mobil Catalytic Material 41 mesostructured matrix, the enhanced homogeneity results from the covalently grafted propyl group in –Si–(CH2)3– that acts as the fundamental spacer which prevents interaction between the attached RuII complex and the silica matrix, and optimal dispersion in the mesopores during the sol–gel polycondensation. Furthermore, the greatly minimized leaching effect of the sensing molecules could be observed in the covalently grafted system. The covalent grafting strategy presented in this paper provides superior optical oxygen sensors with homogeneous distribution, improved sensitivity, and simplified calibration plots.  相似文献   

13.
A new class of bifunctional periodic mesoporous organosilicas (PMOs) composed of organosilicate building blocks with two different silicon sites have been synthesized from the single‐source bifunctional organosilica precursors tris(triethoxysilylethyl)ethoxysilane and bis(triethoxysilylethyl)diethoxysilane, respectively denoted MT3‐PMO and DT2‐PMO. The synthesis of these PMOs is achieved by the co‐assembly of a triblock‐copolymer Pluronic P123 template with the bifunctional organosilica precursor under acid‐catalyzed and inorganic‐salt‐assisted conditions. After template removal through solvent extraction, the MT3‐PMO and DT2‐PMO so obtained show well‐ordered mesopores and display large pore diameters (6–7 nm) and pore volumes (0.6–0.8 cm3 g–1) with a narrow pore‐size distribution and high surface areas (700–800 m3 g–1).  相似文献   

14.
Carbon bridged (C‐PCPDTBT) and silicon‐bridged (Si‐PCPDTBT) dithiophene donor–acceptor copolymers belong to a promising class of low bandgap materials. Their higher field‐effect mobility, as high as 10?2 cm2 V?1 s?1 in pristine films, and their more balanced charge transport in blends with fullerenes make silicon‐bridged materials better candidates for use in photovoltaic devices. Striking morphological changes are observed in polymer:fullerene bulk heterojunctions upon the substitution of the bridging atom. XRD investigation indicates increased π–π stacking in Si‐PCPDTBT compared to the carbon‐bridged analogue. The fluorescence of this polymer and that of its counterpart C‐PCPDTBT indicates that the higher photogeneration achieved in Si‐PCPDTBT:fullerene films (with either [C60]PCBM or [C70]PCBM) can be correlated to the inactivation of a charge‐transfer complex and to a favorable length of the donor–acceptor phase separation. TEM studies of Si‐PCPDTBT:fullerene blended films suggest the formation of an interpenetrating network whose phase distribution is comparable to the one achieved in C‐PCPDTBT:fullerene using 1,8‐octanedithiol as an additive. In order to achieve a balanced hole and electron transport, Si‐PCPDTBT requires a lower fullerene content (between 50 to 60 wt%) than C‐PCPDTBT (more than 70 wt%). The Si‐PCPDTBT:[C70]PCBM OBHJ solar cells deliver power conversion efficiencies of over 5%.  相似文献   

15.
A series of photoresponsive and full‐colored fluorescent conjugated copolymers is synthesized by combining phenylene‐ and thienylene‐based main chains with photochromic dithienylethene (DE) side chains. Solutions and cast films of the polymers exhibit various colored fluorescence in visible wavelengths of 400?700 nm corresponding to emissions of the conjugated main chain. The fluorescence is reversibly photoswitched between emission and quenching through DE photoisomerization using external stimuli from ultraviolet and visible light irradiation. The reprecipitation method with ultrasonication enables the polymers to form spherical aggregates with diameters of 20?70 nm in water. After investigating and comparing the optical properties, the resulting nanosphere solutions are assumed to exist in an intermediate state between an isolated state (i.e., in solution) and an aggregated state in cast film. The majority of the nanosphere solutions also exhibit the same photoswitchable fluorescence behavior as those in the solutions and the cast films. The results demonstrate that the visible fluorescence of the conjugated copolymers is reversibly switchable between emission and quenching using the photoisomerizing DE side chain regardless of the fluorescent colors and the polymer chain aggregation.  相似文献   

16.
Periodic mesoporous organosilica (PMO) thin films have been produced using an evaporation‐induced self‐assembly (EISA) spin‐coating procedure and a cationic surfactant template. The precursors are silsesquioxanes of the type (C2H5O)3Si–R–Si(OC2H5)3 or R′–[Si(OC2H5)3]3 with R = methene (–CH2–), ethylene (–C2H2–), ethene (–C2H4–), 1,4‐phenylene (C6H4), and R′ = 1,3,5‐phenylene (C6H3). The surfactant is successfully removed by solvent extraction or calcination without any significant Si–C bond cleavage of the organic bridging groups R and R′ within the channel walls. The materials have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X‐ray diffraction (PXRD), and 29Si and 13C magic‐angle spinning (MAS) NMR spectroscopy. The d‐spacing of the PMOs is found to be a function of R. Nanoindentation measurements reveal increased mechanical strength and stiffness for the PMOs with R = CH2 and C2H4 compared to silica. Films with different organic‐group content have been prepared using mixtures of silsesquioxane and tetramethylorthosilicate (TMOS) precursors. The dielectric constant (k) is found to decrease with organic content, and values as low as 1.8 have been measured for films thermally treated to cause a “self‐hydrophobizing” bridging‐to‐terminal transformation of the methene to methyl groups with concomitant loss of silanols. Increasing the organic content and thermal treatment also increases the resistance to moisture adsorption in 60 and 80 %‐relative‐humidity (RH) environments. Methene PMO films treated at 500 °C are found to be practically unchanged after five days exposure to 80 % RH. These low dielectric constants, plus the good thermal and mechanical stability and the hydrophobicity suggest the potential utility of these films as low‐k layers in microelectronics.  相似文献   

17.
For organic photovoltaic (OPV) cells based on the bulk heterojunction (BHJ) structure, it remains challenging to rationally control the degree of phase separation and percolation within blends of donors and acceptors to secure optimal charge separation and transport. Reported is a bottom‐up, supramolecular approach to BHJ OPVs wherein tailored hydrogen bonding (H‐bonding) interactions between π‐conjugated electron donor molecules encourage formation of vertically aligned donor π‐stacks while simultaneously suppressing lateral aggregation; the programmed arrangement facilitates fine mixing with fullerene acceptors and efficient charge transport. The approach is illustrated using conventional linear or branched quaterthiophene donor chromophores outfitted with terminal functional groups that are either capable or incapable of self‐complementary H‐bonding. When applied to OPVs, the H‐bond capable donors yield a twofold enhancement in power conversion efficiency relative to the comparator systems, with a maximum external quantum efficiency of 64%. H‐bond promoted assembly results in redshifted absorption (in neat films and donor:C60 blends) and enhanced charge collection efficiency despite disparate donor chromophore structure. Both features positively impact photocurrent and fill factor in OPV devices. Film structural characterization by atomic force microscopy, transmission electron microscopy, and grazing incidence wide angle X‐ray scattering reveals a synergistic interplay of lateral H‐bonding interactions and vertical π‐stacking for directing the favorable morphology of the BHJ.  相似文献   

18.
The synthesis and characterization of a novel silicon–silica nanocomposite material are reported. A self‐assembly method allows the encapsulation of silicon nanoclusters within the channels of a periodic mesoporous silica thin film. The result is the formation of a silicon–silica nanocomposite film with bright, room‐temperature photoluminescence in the visible range, and a nanosecond luminescence lifetime. The properties of the nanocomposite material have been studied by several analytical techniques, which collectively show the existence within the channels of non‐diamondoid‐structure‐type silicon nanoclusters with various hydrogenated silicon sites. It is estimated that the silicon nanoclusters in the silica mesoporous films occupy up to 39 % of the accessible pore volume. The nanocomposite film shows improved resistance to air oxidation compared to crystalline silicon. The high loading and chemical stability to oxidation under ambient conditions are important advantages in terms of the development of silicon‐based light‐emitting diodes from this class of materials.  相似文献   

19.
Using conventional methods to synthesize magnetic nanoparticles (NPs) with uniform size is a challenging task. Moreover, the degradation of magnetic NPs is an obstacle to practical applications. The fabrication of silica‐shielded magnetite NPs on carbon nitride nanotubes (CNNTs) provides a possible route to overcome these problems. While the nitrogen atoms of CNNTs provide selective nucleation sites for NPs of a particular size, the silica layer protects the NPs from oxidation. The morphology and crystal structure of NP–CNNT hybrid material is investigated by transmission electron microscopy (TEM) and X‐ray diffraction. In addition, the atomic nature of the N atoms in the NP–CNNT system is studied by near‐edge X‐ray absorption fine structure spectroscopy (nitrogen K‐edge) and calculations of the partial density of states based on first principles. The structure of the silica‐shielded NP–CNNT system is analyzed by TEM and energy dispersive X‐ray spectroscopy mapping, and their magnetism is measured by vibrating sample and superconducting quantum interference device magnetometers. The silica shielding helps maintain the superparamagnetism of the NPs; without the silica layer, the magnetic properties of NP–CNNT materials significantly degrade over time.  相似文献   

20.
A series of hybrid materials based on chiral nematic mesoporous organosilica (CNMO) films infiltrated with liquid crystalline hydrogen‐bonded assemblies is prepared and characterized with respect to the mutual manipulation of the photonic properties of the host and the liquid‐crystalline behavior of the guest. Detailed differential scanning calorimetry studies reveal the impact of confinement on the mesomorphic behavior of the liquid crystalline assemblies in the pores of the CNMO films. The photonic properties of the chiral nematic mesoporous host can be controlled by changing the temperature or irradiating the films with UV light. These stimuli‐induced phase transitions are accompanied by changes in the orientational order of the mesogens as revealed by 19F NMR spectroscopy. The combination of confinement and changes in the molecular orientation in a unique hybrid material based on hydrogen‐bonded liquid crystals and a porous host with a chiral nematic mesostructure is an interesting concept for the design of optical sensors, reflectors, or filters.  相似文献   

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