Surface Energy of Silica-TEOS-PDMS Ormosils

Inverse gas chromatography (IGC) was applied to characterize the surface energy of organically modified silicates (ormosils) by measuring the interaction of molecular organic probes with the ormosil surface. Ormosils were prepared by the sol-gel method by the reaction of TEOS (tetraethoxysilane), PDMS (polydimethylsiloxane) and different types of silica (Aerosil 130, Aerosil 200 and Aerosil 380). The isosteric heat of adsorption, q _st, and the dispersive component of the surface energy, _s ^D, were estimated by using the retention volume of different nonpolar and polar probes at infinite dilution. The dispersive component shows an increase as the specific surface area of the silica is increased from 29.6 mJ/m² to 51.4 mJ/m² at 60°C. Such values are lower than that obtained for aerosil particles meaning that PDMS chains impede the interaction with silanol groups located on the silica surface. The specific interaction parameter, I^SP, and the enthalpy of specific adsorption, H _a ^SP, of polar probes on the ormosil surface were also measured in order to obtain the acid-base character of ormosil surface. The H _a ^SP, was correlated with the donor, DN, and the acceptor, AN, numbers of the probes to quantify the acidic, K _A, and the basic, K _B, parameters of the substrate surface. The obtained results suggest that the silica particles were covered by PDMS chains in a different way depending on the type of silica used. The values of K _A and K _B suggest that the ormosil surface is amphoteric, with predominantly acceptor electron sites.     

Eine semiempirische Gleichung zur Beschreibung des Lösungsmitteleinflusses auf Statik und Kinetik chemischer Reaktionen. Teil I

A model has been developed for calculating the enthalpy, entropy and free energy change associated with the creation of cavities in a liquid the size of which corresponds to the volume occupied by a solvent molecule. The molar enthalpy change H _cav equals the molar enthalpy of vaporization of the liquid, the free energy change G _cav is given by G _cav=–RT ln (V _m ·p _eq /RT) (V _m =molar volume,p _eq =equilibrium vapor pressure) and is related to the standard free energy of vaporization. This relationship provides an estimate of the free energy of cavity formation required to accomodate a substrate in the liquid. It has been shown, that the free energy of solvation of a substrate can be dissected into different contributions accounting for (1) the concentration dependence of partial molar free energy quantities, (2) the formation of holes in the solvent, (3) the existence of specific, short range solute-solvent interactions and (4) the dielectric polarization of the medium. Application of this concept leads to an equation of the general form G ^S –G ^R =a(DN ^S –DN ^R )+b(AN ^S –AN ^R )+c(G _vp ^oS –G _vp ^oR ), where G represents the free energy of reaction or activation,DN the donor number,AN the acceptor number and G _vp ^o the standard free energy of vaporization of a solventS and a reference solventR, resp.

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Mit 3 Abbildungen     

The kinetics of reaction of copper with substituted benzyl bromides in dipolar aprotic solvents

The reaction of copper with benzyl bromides in dipolar aprotic solvents has been studied. There are no linear or other simple relations between ε, 1/ε, Y, P, n, and the rate of reaction. The activity of the solvent is determined by donor number (DN) in reaction under consideration. The kinetic and thermodynamic parameters of the reaction of copper with benzyl bromide in dimethyl sulfoxide (DMSO) have been clarified. Hammett plots of log (k/k°) vs. the substituent constant σ gave good correlations (ρ = 0.18, S_ρ = 0.02, r = 0.961 in dimethyl sulfoxide and ρ = 0.21, S_ρ = 0.02, r = 0.947 in dimethylacetamide (DMAA)). The structure of the organic group has little effect on the rate of reaction of benzyl bromide with copper. The Hammett ρ value also depends on DN. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 496–501, 2005     

Empirical Hydrogen Bonding Donor (HBD) Parameters of Organic Solvents Using Solvatochromic Probes – A Critical Evaluation

The solvatochromicity of established solvatochromic UV/Vis probes, which appear to be sensitive to the so-called hydrogen bond donor (HBD) property of the solvent, is analysed using the hydroxyl group density of alcoholic solvents D_HBD as a physical parameter in comparison to the pKa, the chemical benchmark for acidity. Reichardt's dye B30 , Kosowers Z-indicator 1-ethyl-4-(methoxycarbonyl) pyridinium iodide ( K ), Kamlet-Tafts α, Dragos S parameter, Catalans SA scale, the cis-dicyano-bis (1,10-phenanthroline) iron II complex (Schilt's Ferrocyphen dye, Fe ) and Gutmann‘s acceptor number (AN) have been investigated. The observed dependencies of the empirical polarity parameters as a function of D_HBD for several alcoholic solvent families requires a ompletely new physicochemical understanding of these established HBD parameters. Only the AN scale (or Fe ) is able to bridge the gap between global polarity and acidity, provided the values are interpreted correctly and applied accordingly.     

Energy Relay from an Unconventional Yellow Dye to CdS/CdSe Quantum Dots for Enhanced Solar Cell Performance

A new design for a quasi‐solid‐state Forster resonance energy transfer (FRET) enabled solar cell with unattached Lucifer yellow (LY) dye molecules as donors and CdS/CdSe quantum dots (QDs) tethered to titania (TiO₂) as acceptors is presented. The Forster radius is experimentally determined to be 5.29 nm. Sequential energy transfer from the LY dye to the QDs and electron transfer from the QDs to TiO₂ is followed by fluorescence quenching and electron lifetime studies. Cells with a donor–acceptor architecture (TiO₂/CdS/CdSe/ZnS‐LY/S^2?‐multi‐walled carbon nanotubes) show a maximum incident photon‐to‐current conversion efficiency of 53 % at 530 nm. This is the highest efficiency among Ru‐dye free FRET‐enabled quantum dot solar cells (QDSCs), and is much higher than the donor or acceptor‐only cells. The FRET‐enhanced solar cell performance over the majority of the visible spectrum paves the way to harnessing the untapped potential of the LY dye as an energy relay fluorophore for the entire gamut of dye sensitized, organic, or hybrid solar cells.     

Regioisomeric Effects on the Electronic Features of Indenothiophene‐Bridged D–π‐A′–A DSSC Sensitizers

Two D–π‐A′–A regioisomers (A‐IDT‐D and D‐IDT‐A) featuring 4,4′‐di‐p‐tolyl‐4 H‐indeno[1,2‐b]‐thiophene as a π linker (π) between the diarylamino donor (D) and the pyrimidine–cyanoacrylic acid acceptor (A′–A) have been successfully synthesized and characterized as efficient sensitizers for the dye‐sensitized solar cells (DSSCs). The different arrangements of the D and A′–A blocks on the unsymmetrical indenothiophene (IDT) core render the dipole of IDT being along (A‐IDT‐D) or opposite (D‐IDT‐A) to the direction of intramolecular (donor‐to‐acceptor) charge transfer, and thus induce variations in the physical properties. The experimental observations correlated well with the theoretical analyses, clearly revealing the trade‐off between the molar extinction coefficient (ε) and the S₀→S₁ transition energy. As a result, a superior ε value was observed for D‐IDT‐A, whereas a bathochromic shift in the absorption occurred in A‐IDT‐D. The larger ε value of D‐IDT‐A together with its more favorable energy level relative to TiO₂ led to a higher power conversion efficiency of 7.41 % for the D‐IDT‐A‐based DSSC, retaining approximately 95 % of the N719‐based DSSC efficiency. This work manifests the clear structure–property relationship for the case of donor and acceptor components being connected by an unsymmetrical π linker and provides insights for molecular engineering of organic sensitizers.     

Computational studies on optoelectronic and charge transfer properties of some perylene‐based donor‐π‐acceptor systems for dye sensitized solar cell applications

We report DFT studies on some perylene‐based dyes for their electron transfer properties in solar cell applications. The study involves modeling of different donor‐π‐acceptor type sensitizers, with perylene as the donor, furan/pyrrole/thiophene as the π‐bridge and cyanoacrylic group as the acceptor. The effect of different π‐bridges and various substituents on the perylene donor was evaluated in terms of opto‐electronic and photovoltaic parameters such as HOMO‐LUMO energy gap, λ_max, light harvesting efficiency(LHE), electron injection efficiency (Ø_inject), excited state dye potential (E^dye*), reorganization energy(λ), and free energy of dye regeneration (). The effect of various substituents on the dye–I₂ interaction and hence recombination process was also evaluated. We found that the furan‐based dimethylamine derivative exhibits a better balance of the various optical and photovoltaic properties. Finally, we evaluated the overall opto‐electronic and transport parameters of the TiO₂‐dye assembly after anchoring the dyes on the model TiO₂ cluster assembly.     

Extraction and preconcentration of tylosin from milk samples through functionalized TiO2 nanoparticles reinforced with a hollow fiber membrane as a novel solid/liquid‐phase microextraction technique

The aim of this study was to introduce a novel, simple, and highly sensitive preparation method for determination of tylosin in different milk samples. In the so‐called functionalized TiO₂ hollow fiber solid/liquid‐phase microextraction method, the acceptor phase is functionalized TiO₂ nanoparticles that are dispersed in the organic solvent and held in the pores and lumen of a porous polypropylene hollow fiber membrane. An effective functionalization of TiO₂ nanoparticles has been done in the presence of aqueous H₂O₂ and a mild acidic ambient under UV irradiation. This novel extraction method showed excellent extraction efficiency and a high enrichment factor (540.2) in comparison with conventional hollow fiber liquid‐phase microextraction. All the experiments were monitored at λ_max = 284 nm using a simple double beam UV‐visible spectrophotometer. A Taguchi orthogonal array experimental design with an OA₁₆ (4⁵) matrix was employed to optimize the factors affecting the efficiency of hollow fiber solid/liquid‐phase microextraction such as pH, stirring rate, salt addition, extraction time, and the volume of donor phase. This developed method was successfully applied for the separation and determination of tylosin in milk samples with a linear concentration range of 0.51–7000 μg/L (r² = 0.991) and 0.21 μg/L as the limit of detection.     

Chromatographic characterisation of ordered mesoporous silicas. Part II: Acceptor–donor properties

The ordered mesoporous siliceous materials: MCM41C16, MCM41C16-SH and MCM41C16-NH₂ (known as MCMs) having different surface functionalities were studied by inverse gas chromatography to characterise their acceptor-donor properties. The DN values denoting the donor number in the Gutmann scale and the AN* values denoting the acceptor number in the Riddle–Fowkes scale have been chosen in the estimation of the electron-acceptor parameter K_A and electron-donor parameter K_D values. The number and kind of the employed adsorbates have an influence on the results obtained. The problem of the number of adsorbates employed has been considered in the light of both results obtained in the present study and the data available in the literature for siliceous adsorbents with randomly ordered structures. Complementary information was obtained by X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy.     

Carbon‐Dot‐Sensitized,Nitrogen‐Doped TiO2 in Mesoporous Silica for Water Decontamination through Nonhydrophobic Enrichment–Degradation Mode

Mesoporous silica synthesized from the cocondensation of tetraethoxysilane and silylated carbon dots containing an amide group has been adopted as the carrier for the in situ growth of TiO₂ through an impregnation–hydrothermal crystallization process. Benefitting from initial complexation between the titania precursor and carbon dot, highly dispersed anatase TiO₂ nanoparticles can be formed inside the mesoporous channel. The hybrid material possesses an ordered hexagonal mesostructure with p6mm symmetry, a high specific surface area (446.27 m² g^?1), large pore volume (0.57 cm³ g^?1), uniform pore size (5.11 nm), and a wide absorption band between λ=300 and 550 nm. TiO₂ nanocrystals are anchored to the carbon dot through Ti?O?N and Ti?O?C bonds, as revealed by X‐ray photoelectron spectroscopy. Moreover, the nitrogen doping of TiO₂ is also verified by the formation of the Ti?N bond. This composite shows excellent adsorption capabilities for 2,4‐dichlorophenol and acid orange 7, with an electron‐deficient aromatic ring, through electron donor–acceptor interactions between the carbon dot and organic compounds instead of the hydrophobic effect, as analyzed by the contact angle analysis. The composite can be photocatalytically recycled through visible‐light irradiation after adsorption. The narrowed band gap, as a result of nitrogen doping, and the photosensitization effect of carbon dots are revealed to be coresponsible for the visible‐light activity of TiO₂. The adsorption capacity does not suffer any clear losses after being recycled three times.     

NMR-spectroscopic studies on solvent electrophilic properties,Part II: Binary aqueous-non aqueous solvent systems

Acceptor numbers have been determined for binary mixtures of water with acetonitrile (AN), dioxane, acetone (AC), pyridine (PY), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), hexamethylphosphoramide (HMPA), methanol, ethanol andi-propyl alcohol. The electrophilic properties of binary aqueous-non aqueous solvent mixtures are determined both by selective solvation and specific solvent-solvent interactions. The variation of the acceptor number as a function of solvent composition is interpreted in terms of the previously determined nucleophilic and electrophilic properties of the pure components and their specific solvent structure.With 6 FiguresIn eq. (1), ^corr means the³¹P chemical shift ofEt ₃PO at concentration zero in a solventS referred to an infinitely dilute solution ofEt ₃PO inn-hexane and corrected for differences in volume susceptibilities betweenS and hexane, ^corr (Et ₃PO·SbCl₅) denotes the corresponding chemical shift value for the adductEt ₃PO·SbCl₅ at infinite dilution in 1,2-dichloroethane which is arbitrarily assigned anAN=100.     

Theoretical characterization and design of small molecule donor material containing naphthodithiophene central unit for efficient organic solar cells

To seek for high‐performance small molecule donor materials used in heterojunction solar cell, six acceptor–donor–acceptor small molecules based on naphtho[2,3‐b:6,7‐b′]dithiophene ( NDT ) units with different acceptor units were designed and characterized using density functional theory and time‐dependent density functional theory. Their geometries, electronic structures, photophysical, and charge transport properties have been scrutinized comparing with the reported donor material NDT(TDPP)₂ ( TDPP = thiophene‐capped diketopyrrolopyrrole). The open circuit voltage (V_oc), energetic driving force(ΔE_L‐L), and exciton binding energy (E_b) were also provided to give an elementary understanding on their cell performance. The results reveal that the frontier molecular orbitals of 3–7 match well with the acceptor material PC₆₁BM , and compounds 3–5 were found to exhibit the comparable performances to 1 and show promising potential in organic solar cells. In particular, comparing with 1 , system 7 with naphthobisthiadiazole acceptor unit displays broader absorption spectrum, higher V_oc, lower E_b, and similar carrier mobility. An in‐depth insight into the nature of the involved excited states based on transition density matrix and charge density difference indicates that all S₁ states are mainly intramolecular charge transfer states with the charge transfer from central NDT unit to bilateral acceptor units, and also imply that the exciton of 7 can be dissociated easily due to its large extent of the charge transfer. In a word, 7 maybe superior to 1 and may act as a promising donor candidate for organic solar cell. © 2013 Wiley Periodicals, Inc.     

Crystallization of titania ultra-fine particles from peroxotitanic acid in aqueous solution in the present of polymer and incorporation into poly(methyl methacylate) via dispersion in organic solvent

We report a novel strategy for incorporation of titanium dioxide (TiO₂) particles, which were crystallized from peroxotitanic acid in the presence of hydrophilic polymer by hydrothermal treatment in aqueous solution, into poly(methyl methacrylate) (PMMA) via dispersion into chloroform. Dispersion of TiO₂ particles into chloroform was achieved by solvent change from water to chloroform in aid of amphiphilic polymer dispersant, poly(N-vinyl pyrrolidone) (PVP), poly(N-vinyl pyrrolidone-co-methyl methacrylate) (PVP-co-PMMA), poly(N-vinyl pyrrolidone-block-methyl methacrylate) (PVP-b-PMMA) through azeotropical removal of water. Incorporation of TiO₂ particles into PMMA was carried out by a casting process of a mixture of TiO₂ particles dispersed with PVP₁₅₄-b-PMMA₁₅₆ in chloroform and PMMA on a glass substrate. Resultant hybrid film containing TiO₂ less than 10 wt.% showed high transparency in visible region attributable to homogeneous dispersion into PMMA matrix. The refractive index of the hybrid films increased with TiO₂ content and agreed with the calculated values.     

New isostructural transition metal complexes with a non‐innocent dithiolate ligand

Three new complexes with 3,6‐dichlorobenzene‐1,2‐dithiol (bdtCl₂), namely methyltriphenylphosphonium bis(3,6‐dichlorobenzene‐1,2‐dithiolato‐κ²S,S′)cobaltate(1−), (C₁₉H₁₈P)[Co(C₆H₂Cl₂S₂)₂], (I), bis(methyltriphenylphosphonium) bis(3,6‐dichlorobenzene‐1,2‐dithiolato‐κ²S,S′)cuprate(2−) dimethyl sulfoxide disolvate, (C₁₉H₁₈P)₂[Cu(C₆H₂Cl₂S₂)₂]·2C₂H₆OS, (II), and methyltriphenylphosphonium bis(3,6‐dichlorobenzene‐1,2‐dithiolato‐κ²S,S′)cuprate(1−), (C₁₉H₁₈P)[Cu(C₆H₂Cl₂S₂)₂], (III), have been synthesized and characterized by single‐crystal X‐ray diffraction. The X‐ray structure analyses of all three complexes confirm that the four donor S atoms form a slightly distorted square‐planar coordination arrangement around the central metal atom. An interesting finding for both the Cu^II and Cu^III complexes, i.e. (II) and (III), respectively, is that the coordination polyhedra are principally the same and differ only slightly with respect to the interatomic distances.     

Electrochemical synthesis and properties of iron–titanium dioxide composite coatings

Deposition of Fe/TiO₂ composite coatings from a colloidal methanesulfonate electrolyte containing titanium dioxide hydrosol was studied. The TiO₂ content in the composite increases with increasing the dispersed phase content and decreasing the current density. Incorporation of TiO₂ particles into the iron matrix resilts in an increase in the microhardness of the deposit. The electroplated Fe/TiO₂ composite coating was used as a heterogeneous photocatalyst for the decomposition of an organic dye under the action of UV radiation.     

Encapsulation of inorganic particles via miniemulsion polymerization. I. Dispersion of titanium dioxide particles in organic media using OLOA 370 as stabilizer

The dispersion of hydrophilic and hydrophobic titanium dioxide (TiO₂) particles in organic media (styrene and cyclohexane) was studied to evaluate the effect of dispersion quality (i.e., size and stability) on the encapsulation efficiencies of subsequent miniemulsion polymerizations. Through screening studies of various block copolymers, OLOA 370 (polybutene–succinimide pentamine) was chosen as the stabilizer for detailed dispersion studies on both types of TiO₂ particles. As a result of strong interactions between the amine end group of the OLOA 370 stabilizer and the hydroxyl groups on the surface of the hydrophilic TiO₂ particles, a good dispersion stability and small particle size (D_v = 39–45 nm) was obtained using 1.0 wt % stabilizer and 20 min of sonification. The dispersions of the hydrophobic TiO₂ particles resulted in a larger average particle size (D_v = 60 nm) and poorer stability. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4419–4430, 2000     

Kinetics of reaction of copper with substituted benzyl chlorides in dipolar aprotic solvents

The reaction of copper with benzyl chlorides in dipolar aprotic solvents has been investigated. The kinetic and thermodynamic parameters of the reaction of copper with benzyl chloride in dimethyl sulfoxide, dimethylacetamide, and hexamethylphosphoramide have been obtained. Hammett plots of log (k/k°) versus the substituent constant σ gave good correlation. The structure of the organic group has little effect on the rate of reaction of benzyl chloride with copper. The kinetic and thermodynamic parameters were correlated with donor number of solvent (DN). The ratio k_RBr/k_RCl and Hammett ρ values provide evidence in favor of the halogen atom transfer mechanism. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 547–555, 2007     

Dye-sensitized solar cells based on bisindolylmaleimide derivatives

Three organic dyes based on bisindolylmaleimide derivatives (I1, I2 and I3) were synthesized and investigated as sensitizers for the application in nanocrystalline TiO₂ solar cells. The indole group, maleimide group and carboxylic group functioned as electron donor, acceptor and anchoring group, respectively. Solar-to-electrical energy conversion efficiencies under simulated amplitude-modulated 1.5 irradiation (100 mW·cm⁻²) of 2.07% were obtained for solar cells based on I2 and of 1.87% and 1.50% for I3 and I1, respectively. The open circuit voltage V _oc was demonstrated to be enhanced by the introduction of dodecyl or benzyl moieties on the indole groups. The nonplanar structure of bisindolylmaleimide was proven to be effective in aggregation resistance. This work suggests that organic sensitizers with maleimide as electron acceptor are promising candidates as organic sensitizers in dye-sensitized solar cells.     

Solvation effects in the electrochemistry of diphenylpicrylhydrazyl

The electrochemistry of diphenylpicrylhydrazyl (DPPH) was studied in nitromethane, nitrobenzene, benzonitrile, acetonitrile, acetone, methanol, ethanol, propanol-2,N,N-dimethylformamide,N,N-dimethylacetamide, and dimethylsulfoxide employing cyclic voltammetric technique. Reversible behaviour was observed for the systemsDPPH/DPPH ⁺ andDPPH/DPPH ^? in all solvents on the platinum microelectrode. The variation of ΔE ^form=(E _oxidation ^form ?E _reduction ^form ) upon solvent can be well described by a complementaryLewis acid—base model for solvent—solute interactions: ΔE ^form=?3.685DN?4.537An+651.84 with a correlation coefficient ofr=0.991 (E ^form stands for formal potential whereasDN andAN are the donor number and the acceptor number). The solvent effect on the position of the spectral absorption ofDPPH is also discussed;v _max values show good linear regression with the π*-parameter introduced byKamlet andTaft.     

Synthesis of OMS Materials and Investigation of Their Acceptor–Donor Characteristics

Three ordered mesoporous siliceous (OMS) materials known as MCM41s—unmodified MCM-41C16 (“C16”), and two MCM41s with different surface functionalities: MCM-41C16-SH (“C16-SH”) and MCM-41C16-NH₂ (“C16-NH₂”)—were synthesized and studied by inverse gas chromatography in order to determine their acceptor–donor properties. The specific retention volumes of nonpolar and polar probes that were chromatographed on these ordered mesoporous silica adsorbents were evaluated under infinite dilution conditions. Two methods were employed to calculate the standard free energy of adsorption, ΔG _ads, of each chromatographed probe on the basis its specific retention volume. These ΔG _ads values were then employed to estimate the van der Waals contribution and the specific contribution of the free surface energy for each MCM41. DN values (donor numbers, based on the Gutmann scale) and AN* values (acceptor numbers, based on the Riddle–Fowkes scale) were employed to determine the values of parameters that characterize the ability of the MCM41s to act as electron acceptors (parameter: K _A) and donors (parameter: K _D). Considering the different compositions of the probes, each of which has different acceptor–donor properties, a new chromatographic test to supplement the Grob test is suggested.