Acetylene and argon adsorption in a supramolecular organic zeolite

The adsorption properties of a new nanoporous organic zeolite with respect to acetylene and Ar were studied by volumetric adsorption analysis, microcalorimetric experiments, and synchrotron high-resolution X-ray powder diffraction. This allowed us to locate the guest molecules inside the host channels and characterize the host-guest interactions.     

Model aluminum-poly(p-phenylenevinylene) interfaces studied by surface raman spectroscopy

Polymeric organic light-emitting diodes (OLEDs) have emerged as inexpensive and versatile alternatives to traditional inorganic-based display technologies. Further advances in this field depend on extending device lifetimes and improving electroluminescence efficiencies, both of which are strongly coupled to the integrity of the electrode/organic contacts. Therefore, the deposition of low-work function metals on organic materials has been extensively studied by X-ray photoelectron spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), and near-edge X-ray adsorption fine structure (NEXAFS) to ascertain information about the chemical and electronic states within the interfacial region. However, to date, the only molecular structural information about metal-organic species formed in these regions has come from fits of theoretical models to existing XPS and UPS data. Very little direct structural information exists about the potential multitude of metal-organic species formed during cathode deposition. We report the use of surface Raman spectroscopy to study the interactions between aluminum and trans-stilbene, a model for poly(p-phenylenevinylene) (PPV). The Raman spectral data suggest preferential formation of covalent Al-C bonds at the vinylene carbons as opposed to the phenyl carbons of PPV.     

Mapping the frontier electronic structures of triphenylamine based organic dyes at TiO2 interfaces

The frontier electronic structures of a series of organic dye molecules containing a triphenylamine moiety, a thiophene moiety and a cyanoacrylic acid moiety have been investigated by photoelectron spectroscopy (PES), X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES) and resonant photoelectron spectroscopy (RPES). The experimental results were compared to electronic structure calculations on the molecules, which are used to confirm and enrich the assignment of the spectra. The approach allows us to experimentally measure and interpret the basic valence energy level structure in the dye, including the highest occupied energy level and how it depends on the interaction between the different units. Based on N 1s X-ray absorption and emission spectra we also obtain insight into the structure of the excited states, the molecular orbital composition and dynamics. Together the results provide an experimentally determined energy level map useful in the design of these types of materials. Included are also results indicating femtosecond charge redistribution at the dye/TiO(2) interface.     

The Electrical Double Layer at Hydrous Manganese Dioxide/Electrolyte Interface

We present here a study of a tetrathiafulvalene derivative, tetrakis(octadecylthio)tetrathiafulvalene (TTFH), arranged in LB films together with a detailed characterization process by means of UV-vis, IR, SEM, and X-ray diffraction that has allowed us to propose a packing model. These films were exposed to iodine vapor and this doping process was carefully followed using UV-vis and IR spectroscopy. The redox properties of the TTFH were studied in both organic solution and LB films. The results have been interpreted in terms of the molecular structure and the LB film architecture. Copyright 2001 Academic Press.     

Structure of cadmium sulfide nanoparticle micelle in aqueous solutions

The structure of cadmium sulfide (CdS) micelle in stable aqueous solution of ethylenediaminetetraacetic acid was determined by dynamic light scattering, small-angle X-ray scattering and neutron scattering. The micelle aggregate is a single CdS nanoparticle with an average size of about 3 nm, the nanoparticle organic shell and the solvation shell are about 1 nm and 5 nm thick, respectively. These parameters were confirmed by the scanning semi-contact atomic force microscopy and powder X-ray diffraction studies of dry micelle cores isolated by high-speed centrifugation. The CdS micelle was correctly described by a simple double-shell model and was found to possess the structure corresponding to CdS quantum dots.     

Construction of High-Density Binuclear Site Catalysts from Double Framework Interfaces at the Cooling Stage

Low-nuclear site catalysts with dual atoms have the potential for applications in energy and catalysis chemistry. Understanding the formation mechanism of dual metal sites is crucial for optimizing local structures and designing desired binuclear sites catalysts. In this study, we demonstrate for the first time the formation process of dual atoms through the pyrolysis of the interface of a double framework using Zn atoms in metal–organic frameworks and Co atoms in covalent organic frameworks. We unambiguously revealed that the cooling stage is the key point to form the binuclear sites by employing the in situ synchrotron radiation X-ray absorption spectrum technique. The binuclear site catalysts show higher activity and selectivity than single dispersed atom catalysts for electrocatalytic oxygen reduction. This work guides us to synthesize and optimize the various binuclear sites for extensive catalytic applications.     

The use of thermo-XRD-analysis in the study of organo-smectite complexes

Summary Thermo-XRD-analysis is applied to identify whether or not the adsorbed organic species penetrates into the interlayer space of the smectites mineral. In this technique an oriented smectite sample is gradually heated to temperatures above the irreversible dehydration of the clay, and after each thermal treatment is diffracted by X-ray at ambient conditions. In the thermal treatment of organo-clays, under air atmosphere at temperatures above 250°C, the organic matter is in part oxidized and charcoal is formed from the organic carbon. In inert atmosphere e.g. under vacuum above 250°C the organic matter is pyrolyzed and besides small molecules, charcoal is formed. If the adsorbed organic compound is located in the interlayer space, the charcoal is formed in that space, preventing the collapse of the clay. A basal spacing of above 1.12 nm suggests that during the adsorption the organic compound penetrated into the interlayer space. Thermo-XRD-analyses of montmorillonite complexes with anilines, fatty acids, alizarinate, protonated Congo red and of complexes of other smectites with acridine orange are described. To obtain information about spacings of the different tactoids that comprise the clay mixture, curve-fitting calculations on the X-ray diffractograms were adapted.     

High-Resolution X-ray Crystallography—An Experimental Method for the Description of Chemical Bonds

By increasing the accuracy of an X-ray analysis, results are obtained which allow one to beyond the location of hydrogen atoms and say something about the distribution of electrons in molecules. Using several examples from organic and organometallic chemistry, the methods, problems, and results of this approach are described.     

The performance of chitosan layer in Au/n-Si sandwich structures as a barrier modifier

This study focused on the structural, optical and electrical features of chitosan organic layer obtained by spin coating technique both on glass and n-Si substrates. XRD results indicated that chitosan has polycrystalline orthorhombic nature. While optical transmittance spectrum of the chitosan organic layer exhibited an increasing tendency in the visible range, band gap energy value was calculated as 4.23 eV for chitosan by UV–Vis spectrometer. Electrical performance of organic chitosan layer in a Schottky device was studied by fabricating of Au/n-Si and Au/chitosan/n-Si devices. The suitability of Au/chitosan/n-Si sandwich devices in optoelectronic applications were tested under dark and illumination conditions. The Au/chitosan/n-Si sandwich device exhibits good photodiode characteristics. Furthermore, the effect of X-ray radiation doses on the electrical properties of the Au/chitosan/n-Si sandwich device was also investigated. In order to get information about electrical characteristics as a function of X-ray radiation doses, Au/chitosan/n-Si sandwich device was exposed to X-ray radiation in same exposure time and various doses. The results highlighted that the performance of the device with chitosan organic interface layer deteriorated with increasing radiation dose. In addition, the transportation mechanism of chitosan based Schottky device was discussed in details.     

Photochemical grafting and patterning of organic monolayers on indium tin oxide substrates

Covalently attached organic layers on indium tin oxide (ITO) surfaces were prepared by the photochemical grafting with 1-alkenes. The surface modification was monitored with static water contact angle, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) measurements. Hydrophobic methyl-terminated ITO surfaces can be obtained via the grafting of tetradec-1-ene, whereas the attachment of ω-functionalized 1-alkenes leads to functionalized ITO surfaces. The use of a C≡C-Ge(CH(3))(3) terminus allows for facile tagging of the surface with an azido group via a one-pot deprotection/click reaction, resulting in bio/electronically active interfaces. The combination of nonaggressive chemicals (alkenes), mild reaction conditions (room temperature), and a light-induced grafting that facilitates the direct patterning of organic layers makes this simple approach highly promising for the development of ITO-based (bio)electronic devices.     

Chemistry in solution: recent techniques and applications using soft X-ray spectroscopy

The aim of a more precise knowledge about molecular structures and the nature of chemical bonds is the driving force behind the development of numerous experimental methods and theories. Recent soft X-ray based techniques provide novel opportunities for tackling the structure and the dynamics of chemical and biochemical systems in solution. In our research group we are developing experimental methods for mapping the electronic structure and dynamics of molecular systems in solution during bond-building and breaking using soft X-ray absorption and emission spectroscopy. The combination of such recent developments with conventional spectroscopy as well as theoretical modeling allows us to address open questions about hydrogen bonds, thermodynamics and active centers of biological systems. Based on the core-hole clock and pump-probe spectroscopy dynamics on the time scale from sub-femtoseconds up to picoseconds can be revealed.     

Microwave synthesis and characterization of Co-ferrite nanoparticles

Stable CoFe(2)O(4) nanoparticles have been obtained by co-precipitation using a microwave heating system. Transmission electron microscopy images analysis shows an agglomeration of particles with an average size of about 5 nm, and X-ray diffraction reveals the presence of a pure ferrite nanocrystalline phase. X-ray photoelectron spectroscopy and thermal gravimetric analysis show the presence of organic matter in the range of about 16 wt%. The magnetic response in DC fields is typical for an assembly of single-domain particles. The measured saturation magnetization is slightly larger than the bulk value, probably due to the presence of small amounts of Co and Fe. AC magnetization data indicate the presence of magnetic interactions between the nanoparticles.     

Structure,dynamics, and solvation in a disordered metal–organic coordination polymer: a multiscale study

Metal–organic coordination polymers are a growing class of technologically-important materials in which transition metal ions are connected by multitopic organic chelators to form a 3-D network structure. While the structures of many highly-ordered metal–organic frameworks have been determined, far less structural information is available about the more common disordered materials. Our study combines pair distribution function analysis from total X-ray scattering, ab initio quantum mechanical calculations, and all-atom molecular dynamics to explore the structure and dynamics of a poorly-ordered branched coordination polymer. The polymer structure is highly flexible and dynamic, and is dramatically affected by its solvation state, a finding with far-reaching implications for the incorporation of coordination polymers into nanocomposite materials.     

Characterization of porosity in organic and metal-organic macrocycles by hyperpolarized 129Xe NMR spectroscopy

Hyperpolarized (129)Xe NMR spectroscopy is used to establish the solid-state porosity of shape-persistent macrocycles with either an organic or metal-organic framework. These studies show that even upon removal of cocrystallized solvent molecules, the macrocycles maintain a porous or channeled structure. The technique can provide valuable information about systems for which X-ray crystallographic analysis is not feasible. [structure: see text]     

Determination of Organic Acids in Xylem Sap of Cucumber: Effect of Lead Contamination

Lead, iron, and organic acid concentrations were determined in low-volume xylem sap samples of cucumbers grown in both “lead-free” and lead-contaminated nutrient solutions containing either Fe-citrate or Fe-EDTA by total reflection X-ray fluorescence spectrometry (iron and lead), graphite furnace atomic absorption spectrometry (lead), and reversed-phase high-performance liquid chromatography (organic acids). Three acids of the Krebs cycle—citric, fumaric, and malic acids—were detected and measured. In presence of Fe-citrate the lead contamination results in about three times higher organic acid production in the cucumber compared with the uncontaminated plants. At the same time the amount of transported iron decreases with about 20%. In presence of Fe-EDTA, the same amount of lead leads to a small change in organic acid production; however, the uptake and the transport processes of iron are considerably hindered (35%). Lead transport in the xylem channel was more than one order of magnitude higher when iron was added to the nutrient solution as citrate instead of EDTA complex. These phenomena can be attributed to the participation of the organic acids in the translocation processes of the metals investigated.     

Self-assembly morphology and packing structures depend on the ‘head’ of organic cations anchored on polyoxometalate anions in hybrids

Two organic-polyoxometalates (organic-POMs) hybrids were constructed by fan-shaped 1-methyl-3-[3, 4, 5-tris(octadecyloxy) benzyl]imidazolium salts (labelled as I–Cl) and triethyl-[3, 4, 5-tris (octadecyloxy) benzyl] ammonium salts (labelled as Q–Cl) and Keggin anions [SiW₁₂O₄₀]^4? by electrostatic interaction. Self-assembled behaviours of two aggregates in organic solvent and solid state were investigated in detail by scanning electron microscopy, transmission electron microscopy and X-ray analysis. The mixed solution of chloroform–methanol or chloroform–acetone provided the stable environment for aggregates and aggregates showed a uniform micron size. X-ray analysis results showed that flower-like aggregates morphology of I₄[SiW₁₂O₄₀] based on imidazole ring as ‘head’ in organic cations was formed by the stacking of multilamellar discs and kept the lamellar structure in solid state. Bulk thorn spheres appeared in Q₄[SiW₁₂O₄₀] aggregates, which were formed by closely interspersed of lots flatted blocks with hexagonal structure characteristics in solid state. The comprehension for the self-assembly morphology and solid structure of organic-polyoxometalate hybrids would help us to use easily modified organic moiety and functional inorganic polyoxoanions as blocks to build novel and giant supramolecular architecture.     

新型非线性光学杂化材料结构与性能的研究

由硅烷染料ASD与钛酸四正丁酯在酸性条件下共水解、缩合得到杂化材料,利用透射电镜(TEM)和X射线能量色散谱仪(EDS)进行分析,结果表明,杂化溶胶粒子是由硅和钛的化合物组成的球形纳米粒子.由一维刚性取向气体模型计算杂化材料膜再极化后的二阶非线性光学系数χ⁽²⁾为1.43×10^-7esu.差示扫描量热法(DSC)测得杂化材料的玻璃化温度可达469K;用紫外-可见光谱对杂化膜在极化前后的取向及取向稳定性进行了研究.用原子力显微镜(AFM)和X射线衍射(XRD)研究了材料在极化过程中的结晶行为和微观结构对生色团取向稳定性的影响,初次在这种极化后的膜中观察到了介观结构.     

Crystallography Aided by Atomic Core-Level Binding Energies: Proton Transfer versus Hydrogen Bonding in Organic Crystal Structures

Ionic bond or hydrogen bridge? Br?nsted proton transfer to nitrogen acceptors in organic crystals causes strong N1s core-level binding energy shifts. A study of 15 organic cocrystal and salt systems shows that standard X-ray photoelectron spectroscopy (XPS) can be used as a complementary method to X-ray crystallography for distinguishing proton transfer from H-bonding in organic condensed matter.     

New Methods and Results in the Study of Polyacids

The present status of research on condensed vanadic, molybdic, and tungstic acids is reviewed. Information about the structure and formation of polyanions can be obtained by X-ray analysis and from nuclear magnetic resonance, infrared, and Raman spectra, as well as from complex formation in aqueous solution. Salts of the polyacids can be prepared in organic solvents by hydrolysis of esters of the metal oxoacids.     

Ligand effects on the size and purity of Pd nanoparticles

Palladium nanoparticles (Pd-NPs) were prepared by a single-phase reduction of palladium acetate in the presence of different organic thiol ligands. Sizes, size distributions and crystallinity of the Pd-NPs were determined by high resolution transmission electron microscopy (HR-TEM) and powder X-ray diffraction (XRD) while thermogravimetric analysis coupled with mass spectroscopy (TGA-MS) was employed to measure their organic ligand to palladium ratios and to quantify contaminants. No systematic effect of the different ligands on the size and purity of the Pd-NPs was observed but 1^st-generation Frechet dendron thiols had an about 4 times larger foot-print at the surface of the NPs than the other thiol ligands.