Electrocatalytic construction of the C–N bond from the derivates of CO2 and N2

Electrochemical synthesis of C-N bond-containing compounds(e.g.,urea,amino acid,amide,amine,and their derivates)from CO₂/N₂and their derivates is emerging as a promising sustainable strategy[1-7].CO₂and its derived products,CO,HCOOH,(COOH)₂,etc.,could serve as carbon sources(Figure 1)[8].N₂,making up 80%of air,is an appealing nitrogen source.However,the low solubility of N2 and the high dissociation energy for the N≡N bond limit its application.     

Synthesis and properties of a blue bipolar indenofluorene emitter based on a D-π-A design

Through a rational design, a novel Donor-Acceptor π-conjugated (D-π-A) blue fluorescent indenofluorene dye, DA-DSF-IF, has been synthesized for application in single-layer Small Molecule Organic Light Emitting Diodes (SMOLEDs). This new blue emitter possesses bipolar properties as well as good morphological and emission color stabilities and has been successfully used in a blue emitting single-layer SMOLED, with performances impressively magnified compared to a nonbipolar indenofluorene emitter.     

Structural and photophysical studies of triphenylamine-based nonlinear optical dyes: effects of π-linker moieties on the D-π-A structure

In this work, a series of eight metal-free organic dyes based on triphenylamine as a donor and cyanoacetic acid as an acceptor of electrons with the donor-π-acceptor structure were studied by DFT and TD-DFT methods. Their electronic properties, absorption spectra, and molecular nonlinear optical (NLO) responses have been analyzed and reported. The influence of the change of π-conjugated linker on the electrochemical and photophysical properties of these metal-free organic dyes has been investigated and discussed in detail. The energy gap decreases by going from L1 to L8, which causes a large NLO response for the studied dyes. The natural bond orbital (NBO) analysis reveals that the separation of charge occurred upon photoexcitation and the electrons moved from the donor to the acceptor moiety. A high NLO response reveals that this kind of metal-free organic dyes has eye-catching and remarkably large first hyperpolarizability β_tot values, especially for L7 ((E)-2-cyano-3-(3-((E)-2-(3-((E)-4-(diphenylamino)styryl)benzo[c]thiophen-1-yl)vinyl)benzo [c]thiophen-1-yl)acrylic acid) and L8 ((E)-2-cyano-3-(7-((E)-2-(7-((E)-4-(diphenylamino)styryl)thieno[3,4-b]pyrazin-5-yl)vinyl)thieno[3,4-b]pyrazin-5-yl)acrylic acid) with 150423.50 (a.u) and 202773.63 (a.u), respectively. Our research has been carried out to extend the conjugation of organic materials by controlling their π-conjugated linker to design new appealing NLO compounds. This study shows that these dyes are promising and have special properties for modern hi-tech applications such as solar cells, transistors, and organic light-emitting diodes (OLEDs), and even these properties can be adjusted and enhanced by the incorporation of the benzothiophene or thienopyrazine derivatives as a bridge so as to improve from L7 to L8.     

Effects of structure and electronic properties of D-π-A organic dyes on photovoltaic performance of dye-sensitized solar cells

Herein,we examine the performance of dye-sensitized solar cells containing five D-π-A organic dyes designed by systematic modification of π-bridge size and geometric structure.Each dye has a simple push-pull structure with a triarylamino group as an electron donor,bithiophene-4,4-dimethyl-4 H-cyclopenta 1,2-b:5,4-b’]dithiophene(M11),4,4-dimethyl-4 H-cyclopenta[1,2-b:5,4-b’]dithiophenethiophene(M12),thiophene-4,4-dimethyl-4 H-cyclopenta[1,2-b:5,4-b’]dithiophene(M13),4,4-dimethyl-4 H-cyclopenta[1,2-b:5,4-b’]dithiophene-benzene(M14),and 4,4-dimethyl-4 H-cyclopenta[1,2-b:5,4-b’]dithiophene(M15)units asπ-bridges,and cyanoacrylic acid as an electron acceptor/anchor.The extension of theπ-bridge linkage favors wide-range absorption but,because of the concomitant molecular volume increase,hinders the efficient adsorption of dyes on the TiO₂ film surface.Hence,higher loadings are achieved for smaller dye molecules,resulting in(i)a shift of the TiO₂ conduction band edge to more negative values,(ii)a greater photocurrent,and(iii)suppressed charge recombination between the photoanode and the redox couple in the electrolyte.Consequently,under one-sun equivalent illumination(AM 1.5 G,100 mW/cm²),the highest photovoltage,photocurrent,and conversion efficiency(η=7.19%)are observed for M15,which has the smallest molecular volume among M series dyes.     

Impact of structural features on pigment properties of α-Fe2O3 haematite

Various α-Fe₂O₃ haematite samples were synthesized by precipitation routes (under standard or hydrothermal conditions) followed by thermal treatments under air. The trigonal distortion (C_3v point group) of the Fe³⁺ octahedral sites, which depends on the synthesis route and thermal treatment, was investigated by X-ray diffraction, Mössbauer spectroscopy and visible-near infrared (Vis-NIR) spectroscopy. The correlation between diffuse reflectance spectra and structural features of the haematite samples is reported and discussed herein. The slight increase of the average distortion of the Fe³⁺ octahedral sites, which depends on the annealing temperature of the precipitated sample, directly linked to the crystallite size, contrasts with the larger reduction of the sites distortion for the compound prepared by hydrothermal route due to the occurrence of hydroxyl groups substituted for O²⁻ anions as well as Fe³⁺ cationic vacancies. On a local point of view, as shown by Mössbauer spectroscopy, the Fe³⁺ octahedral sites distortion decreases from the centre towards the surface of the grains. Then the smaller the grain size, the lower the average site distortion. Finally, the reduction of the octahedral distortion was directly correlated to the two FeO charge transfer bands in the visible range and the colour of as-prepared haematites.     

Effects of external electric field and self-aggregations on conformational transition and optical properties of azobenzene-based D-π-A type chromophore in THF solution

The influence of environments (THF solvents and electric field) and molecular self-aggregations on the structure and optical properties of 4-(4-hydroxyphenylazo)nitrobenzene has been investigated by molecular dynamics (MD) simulations and quantum chemical calculations. Long-range electrostatic effects and the hydrogen bond interactions between the solute and the THF solvent molecules lead to the augments of nonlinear optical (NLO) response by about two times from the gas phase to THF solution, accompanied by considerable red-shift of more than 40 nm in the maximum absorption wavelengths of the ground (S(0)) and low-lying excited states (S(1), S(2), and S(3)). The solvated chromophore reorients quickly (within 300 ps) under external electric field of 1.0 V/nm, even when the direction of the applied electric field is antiparallel to the dipole moment of the solute. Nonequilibrium MD simulations demonstrate that the light-induced cis-trans isomerization in THF solution and external electric field need longer relaxation time (about 1.0 ps) than that in gas phase (about 500 fs). The dipole-dipole interactions and intermolecular hydrogen bonds facilitate the self-aggregations of solute molecules in solution. The V-shaped dimer exhibits higher hyperpolarizability value by about 1.2 times of the monomer, whereas the antiparallel alignment leads to a cancellation of dipole moment and hence dramatic decrease in hyperpolarizability (one-third of the monomer). However, the Boltzmann-weighted contribution to hyperpolarizability from these two aggregations (with 82% V-shaped and 18% antiparallel) is close to that of the monomer. Orientations of D-π-A dipoles in various environments and molecular aggregations are important to modulate the optical properties of materials.     

New phosphoroamidate compounds: Synthesis,structural characterization and studies on ZnCl2 assisted hydrolysis of the P–N bond

A variety of phosphorodiamidate compounds were synthesized from the corresponding phosphorodichloridate intermediates and phosphorus oxychloride. These were completely characterized using different spectroscopic methods and single crystal X-ray diffraction studies on one of them. Studies revealed that water in the presence of a mild Lewis acid like ZnCl₂ was found to assist the hydrolysis of the P–N linkage. The proof of this concept was effectively realized through the hydrolysis of hexamethylphosphoramide.     

Solubility of β-carotene in ethanol- and triolein-modified CO2

Modification of an experimental device and methodology improved speed and reproducibility of measurement of solubility of β-carotene in pure and modified SuperCritical (SC) CO₂ at (313 to 333) K. Solubilities of β-carotene in pure CO₂ at (17 to 34) MPa ranged (0.17 to 1.06) μmol/mol and agreed with values reported in literature. The solubility of β-carotene in CO₂ modified with (1.2 to 1.6) % mol ethanol increased by a factor of 1.7 to 3.0 as compared to its solubility in pure CO₂ under equivalent conditions. The concentration of triolein in equilibrated ternary (CO₂ + β-carotene + triolein) mixtures having excess triolein reached values (0.01 to 0.39) mmol/mol corresponding to its solubility in pure SC CO₂ under equivalent conditions. Under these conditions, the solubility of β-carotene in triolein-modified CO₂ increased by a factor of up to 4.0 in relation with its solubility in pure CO₂ at comparable system temperature and pressure, reaching an uppermost value of 3.3 μmol/mol at 333 K and 32 MPa. Unlike in the case of ethanol, where enhancements in solubility where relatively independent on system conditions, solubility enhancements using triolein as co-solvent increased markedly with system pressure, being larger than using (1.2 to 1.6) % mol ethanol at about (24 to 28) MPa, depending on system temperature. The increase in the solubility β-carotene in SC CO₂ as a result of using ethanol or triolein as co-solvent apparently does not depend on the increase in density associated with the dissolution of the co-solvent in CO₂. Enhancements may be due to an increase in the polarizability of SC CO₂, which possibly growths markedly as triolein dissolves in it when the system pressure becomes higher.     

[RuCl2(p-cymene)2]2 catalyzed cross dehydrogenative coupling (CDC) toward xanthone and fluorenone analogs through intramolecular C–H bond functionalization reaction

A synthetic approach toward xanthone and fluorenone derivatives through ruthenium catalyzed intra-molecular C–H bond functionalization using an external oxidant has been developed. In the presence of [RuCl₂(p-cymene)₂]₂, a variety of substituted ortho-aryloxy/aryl benzaldehydes underwent cross dehydrogenative coupling to afford the corresponding analogs in moderate to good yields.     

Effects of sugar ring puckering, anti-syn interconversion and intramolecular interactions on N-glycosidic bond cleavage in 3-methyl-2��-deoxyadenosine and 2��-deoxyadenosine

The effects of structural parameters and intramolecular interactions on N-glycosidic bond length in 3-methyl-2??- deoxyadenosine (3MDA) and 2??-deoxyadenosine (DA) were investigated employing quantum mechanical methods. All calculations were performed at B3LYP/6-311++G** level in the gas phase. The N-glycosidic bond length strongly depends on sugar configuration; it is shorter in syn conformation relative to anti in many cases where they have the same sugar ring configuration. The sugar conformation can influence the N-glycosidic bond through interaction with the O4?? atom. The impact of intramolecular improper hydrogen bonds and H-H bonding interactions on N-glycosidic bond length was investigated in DA and 3MDA and their modeled structures. Improper hydrogen bonds decrease N-glycosidic bond length while H-H bonding interactions increase it.     

Electrophysical properties of materials based on BaGdCo2O5 + δ

The phase composition, linear thermal expansion coefficient, electroconductivity (in the temperature interval 600–900°C and partial pressures of oxygen 10⁻⁵–0.21 atm) of solid-oxide materials based on gadolinium-barium cobaltite doped with 3d-elements BaGdCo_{2 − x} Me _x O_{5 + δ}, Me = Cu, Fe; x = 0.0, 0.2, …, 2.0 were investigated. The homogeneity regions of samples were established by means of X-ray phase analysis. It was shown that the linear thermal expansion coefficient of cobaltite decreases with an increase in the copper or iron concentration. It was established that the electroconductivity of BaGdCo_{2 − x} Me _x O_{5 + δ} decreases with an increase in x. We concluded that upon a decrease in p(O₂), the electroconductivity of samples first decreases and then reaches a horizontal plateau.     

A comparison study on Raman scattering properties of α- and β-MnO2

In this comment to a recent paper [Anal. Chim. Acta 585 (2007) 241-245], we report a comparison study on Mn oxide-related compounds with different crystallographic forms, which distinguish between β-MnO₂ and α-MnO₂ type materials via Raman scattering (RS) spectroscopy. The tetragonal rutile-type β-MnO₂ is characterized by a RS band at ∼667 cm⁻¹ of symmetry A_1g, whereas the α-MnO₂ type materials feature two main RS contributions at about 574 and 634 cm⁻¹, belonging to A_g spectroscopic species of a tetragonal hollandite-type framework. These data represent a clear signature for identifying β-MnO₂ and α-MnO₂ type materials via RS spectroscopy.     

Online NMR spectroscopic study of species distribution in MEA–H2O–CO2 and DEA–H2O–CO2

Quantitative online NMR spectroscopy was used for studying the species distribution in solutions of carbon dioxide in aqueous monoethanolamine (MEA) and diethanolamine (DEA). The mass fraction of the amine in the unloaded solution was 0.2 and 0.3 g/g, respectively, the carbon dioxide loading was up to 1.1 ??molCO₂/molamine$1.1\text{\hspace{0.17em}??}\text{mo}{\text{l}}_{\text{C}{\text{O}}_2}/\text{mo}{\text{l}}_{\text{amine}}$, temperatures were between 293 and 353 K. A special apparatus was designed that allows preparing the mixtures gravimetrically and applying pressures up to 25 bar to keep the carbon dioxide in solution. It was coupled to a 400 MHz NMR spectrometer by heated capillaries. By using both ¹H and ¹³C NMR spectroscopy quantitative information on the concentrations of the following species were obtained: amine, carbamate, bicarbonate, and carbon dioxide. Due to the fast proton transfer between molecular and protonated amine, only the sum of their concentrations can be determined. Furthermore, a byproduct, 2-oxazolidone, was observed and quantified. The experimental data were used for developing a thermodynamic model of the studied electrolyte solutions based on the extended Pitzer G^E-model. In the model development, also vapor–liquid equilibrium data from the literature were included. The model gives reliable results both for the species distribution and the vapor–liquid equilibrium of the studied mixtures.     

Vapor phase methylation of pyridine with CO?H2 and CO2?H2 over a Ni catalyst

Pyridine was methylated selectively to 2-picoline with CO−H₂ and with CO₂−H₂ over a Ni catalyst. 2,6-lutidine was producedvia the methylation of 2-picoline.     

The effect of preparation method on the defect structure and luminescence properties of γ-Al2O3

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Selective oxidation of methanol on V2O5 and V2O5?MoO3 supported on montrmorillonite

Methanol oxidation on V₂O₅ and V₂O₅–MoO₃ catalysts supported on montmorillonite has been studied in the temperature range of 250–500°C. The V₂O₅–MoO₃ containing sample shows higher selectivity towards formaldehyde formation than the V₂O₅ catalyst.     

First example of intramolecular [2π + 2π] alkene-arene photocyclization in the chromone series and its synthetic utility

Diels-Alder adducts of chromones are shown to undergo an intramolecular [2_π+2_π] alkene-arene photocyclization, leading to a versatile polycyclic diene, which is capable of dimerization or can be introduced into a high-yielding photoprotolytic oxametathetic sequence. This allows for an expeditious growth of molecular complexity over a few experimentally simple steps with stereochemistry being defined and locked at the very first Diels-Alder step. The overall reaction can potentially be utilized in diversity-oriented synthesis as it allows for three or more diversity inputs furnishing novel unique polycyclic scaffolds, which can readily be decorated with a variety of functionalities and aromatic/heterocyclic pendants.     

Crystal structure and thermal properties of Na2[ReCl6]·6H2O

The crystal structure of Na₂[ReCl₆]·6H₂O is determined. The crystallographic characteristics are as follows: a = 6.6955(2) ?, b = 7.0926(2) ?, c = 8.3667(3) ?; α = 102.567(1)°, β = 98.853(2)°, γ = 107.236(1)°; V = 360.08(2) ?³, P-1 space group, Z = 1, d _x = 2.550 g/cm³. The thermal properties of Na₂[ReCl₆]·6H₂O are studied in the hydrogen atmosphere. During the thermolysis of Na₂[ReCl₆]_0.50[PtCl₆]_0.50·6H₂O double complex salt in the hydrogen atmosphere, Re _x Pt_1−x nanocrystalline solid solutions were obtained.     

Influence of Sn and Sn/Mg doping on structural features and visible absorption properties of α-Fe2O3 hematite

Pure, Sn-doped and Mg/Sn co-doped α-Fe₂O₃ hematite samples were synthesized by precipitation process. Fe₂O₃ is the most popular red mineral pigment which is used largely in traditional ceramics, tar and concrete. The compounds were characterized by powder X-ray diffraction (XRD), scanning transmission electronic microscopy (energy dispersive X-ray cartography), Mössbauer spectroscopy, magnetic investigations versus temperature and visible-NIR spectroscopy. Both ⁵⁷Fe and ¹¹⁹Sn Mössbauer analyses combined with rietveld XRD refinements are the ideal techniques to characterize tin-iron oxides. Hence, thanks to these techniques it was shown how the synthesis temperature influences directly the grain size and the dopants concentration limit which can be incorporated into the host hematite matrix. The stabilization of these tetravalent and divalent dopants into the hematite framework leads to reduce the crystal growth and to limit the (AF) ordering due to the formation of cationic vacancies. The study of the Morin magnetic transition emphasizes this demonstration. In a second part, the influence of the dopants incorporation on the material color was investigated in order to show which key parameters allow improving the red color saturation of iron oxides. In order to improve the red color of the hematites, it was shown that the introduction of cationic vacancies—limiting the octahedral distortion thanks to the interruption of the dissymmetric metal-metal orbital coupling—is the key point. Vacancies are created by Sn⁴⁺, doping for an increase of the introduced Sn⁴⁺ concentration; it acts to the detriment of the color saturation.