A novel synthesis route for brookite rich titanium dioxide photocatalyst involving organic intermediate

Journal of Sol-Gel Science and Technology - High temperature stable brookite rich titanium dioxide of average crystallite size 20&;nbsp;nm has been prepared by a novel aqueous sol–gel...     

Synthesis,structural, electrochemical,and photophysical properties of 4,2′‐thiopyrylogens – a novel class of sensitizers for photoinduced electron transfer reactions

The first three examples of the thioanalog of the 4,2′‐pyrylogen ring system are reported. The influence of the sulfur atom on the structural, electrochemical, and photophysical behavior of this ring system is discussed. In addition, these 4,2′‐thiopyrylogens are compared to their previously reported 4,4′‐isomers and their 4,4′‐ and 4,2′‐oxygen analogs. Copyright © 2010 John Wiley & Sons, Ltd.     

Triplet photochemistry within zeolites through heavy atom effect, sensitization and light atom effect

Methods to generate triplets of organic molecules within zeolites have been established by employing the Zimmerman rearrangement of barrelenes, oxa-di-π-methane rearrangement of β,γ-unsaturated ketones and photodimerization of acenaphthylene as probe reactions. The two methods, heavy cation effect and triplet sensitization, are well established solution techniques and these work well within zeolites. The Zimmerman rearrangement of dibenzobarrelene is enhanced even within Li⁺ and Na⁺ exchanged zeolites and these are believed to be the result of slowing of the rearrangement to dibenzocyclooctatetraene from S₁ through cation-π interaction. The methods described here provide an opportunity to explore the control afforded by the zeolite environment on triplet reactions.     

Relaxation kinetics of Sm: Ce-doped CaS phosphors

Different samples of calcium sulphide (CaS):CaS(Sm) and CaS(Sm,Ce) phosphors have been prepared. To study the phosphorescence decay systematically, the samples were excited to a saturation using 259 nm line of xenon lamp and phosphorescence emission was monitored for a wavelength 569 nm of samarium. The trap depth has been evaluated by analyzing the decay curves. The observed decay could be explained satisfactorily by assuming a superposition scheme. The thermoluminescence properties of the doped CaS phosphors are also investigated in detail by computerized deconvolution technique of the glow curves obtained by UV irradiation.     

Infrared spectrum of ferroelectric lithium hydrazinium sulphate [Li (N2H5) SO4]

Dielectric observations on lithium hydrazinium sulphate have shown earlier that it is ferroelectric over a range of temperatures from below ?15° C. to above 80° C. and a new type of hydrogen bond rearrangement which would allow the protons to migrate along the chain has also been suggested by others. The infrared spectrum of LiH _z S in the form of mull and as single crystal sections parallel and perpendicular to the ‘C’ axis exhibit about 21 well-defined absorption maxima. The position and the width of the maxima agree with the known structure of the crystal according to which the hydrazine group exists in the form of the hydrazinium ion, NH₂·NH ₃ ⁺ and the observed N⁺-H frequencies agree better with the new correlation curve given by R. S. Krishnan and K. Krishnan (1964). However it has been pointed out that from a comparative study of the new infrared spectra of hydrazonium sulphate and lithium ammonium sulphate that the absorption band at 969 cm.^?1 is due to N-N stretching vibration and that the fairly intense band between 2050–2170 cm.^?1 is due to the bending vibrations of the NH ₃ ⁺ group.     

Infrared absorption spectra of single crystals of glycine silver nitrate and monoglycine nitrate

The infrared absorption spectra of glycine silver nitrate (GAgNO₃) and glycine nitrate (GHNO₃) show that the glycine group exists completely in the zwitter ion form in the former and in both forms in the latter. The spectrum of GAgNO₃ at liquid air temperature did not reveal any striking change which can be attributed to a freezing of the rapid reorientation of the NH ₃ ⁺ group taking place at higher temperatures. The position of the COO^? stretching frequencies indicate that this group is co-ordinated only weakly to the Ag⁺ ion. The summation frequencies reported by Schroeder, Wier and Lippincott (1962) for AgNO₃ were not observed in the present study on GAgNO₃. It shows however that ferroelectricity in GAgNO₃ is in all probability due to the motion of the Ag⁺ ion in the oxygen co-ordination polyhedron and is not directly connected with the ordering of the hydrogen bonds below Curie point.     

Antiwetting silica–gelatin nanohybrid and transparent nano coatings synthesised through an aqueous sol–gel process

Hydrophobic silica-biopolymer hybrid has been synthesised using colloidal silica as the precursor for silica, gelatin as the biopolymer counterpart and vinyltrimethoxysilane as the surface modifier through a sol–gel method. The precursor sol was coated on glass substrates and further investigated for the extent of chemical modification, thermal degradation, hydrophobicity, particle size and transparency in the UV-Visible region. Stereomicrographs clearly indicate the water repellent nature of the hybrid coatings with respect to a water drop. FTIR was used to follow the presence of vinyl groups that impart hydrophobicity to the resultant hybrids. By varying the concentration of functionalizing agent, the extent of hydrophobic property could been tailored. The optimum concentration for effective surface modification of the silica–gelatin hybrid is about 50 wt%. Nearly 100% optical transmittance was obtained for silica–VTMS–gelatin hybrid coatings on glass substrates and this may have potential applications in optical devices and also for transparent biocompatible hydrophobic coatings on biological substrates such as leather.     

Optimization of the catalytic asymmetric addition of nitroalkanes to cyclic enones with trans-4,5-methano-L-proline

[reaction: see text] The conjugate addition of symmetrical 2-nitroalkanes to 2-cycloalkenones catalyzed by trans-4,5-methano-l-proline proceeds with >99% ee and excellent chemical yields. 1-Nitroalkanes afford diastereomeric syn/anti products that can be separated with good individual enantioselectivities. Proline hydroxamic acid and its trans-4,5-methano -l-proline hydroxamic acid are also effective organocatalysts in the addition of 2-nitropropane to 2-cyclohexenone (75% and 81% ee, respectively).     

Secondary alpha isotope effects on deuterium tunneling in triplet o-methylanthrones: extraordinary sensitivity to barrier width

The rates of deuterium transfer in the photoenolization of triplet 1,4-dimethyl-10H-anthracen-9-one (1) with varying degrees of deuterium label in their methyl groups (1-d3, 1-d2, and 1-d) have been investigated as a function of temperature between 5 and 77 K. Measurable rate constants in the case of 1-d3 and 1-d2 were used to construct Arrhenius plots which illustrate the expected curvature and leveling off of rate constant versus temperature. The difference in tunneling rate constants of 1-d3 and 1-d2 yields a tunneling isotope effect, TIE = 2.4, which is attributed to the secondary alpha isotopic substitution. Density functional theory (DFT, B3LYP/6-31G*) calculations were carried out to obtain structural and energetic information for the H(D) transfer along the triplet state zero-point energy levels. The temperature dependence of the rate constants for each isotopologue was simulated with a model that considers the frequency of the C-D stretching mode and the quantum mechanical permeability determined from calculated energy parameters. The model suggests that a difference in barrier width of only 0.015 A between 1-d3 and 1-d2 leads to the observed 2-fold difference between tunneling rates.     

Vibrational and electronic spectra of alkali halides doped with CrO42− ions

The i.r. spectra of alkali halides doped with FrO₄^2? ions are very sensitive to the concentration of background divalent impurities. Highly pure crystals containing CrO₄^2? ions show a 5 line i.r. spectrum in the v₃ stretch frequency region. One of these lines is attributed to CrO₄^2? ions in perfect crystal surroundings having T_d symmetry and the other 4 lines are attributed to C_s symmetry produced by a charge compensating anion vacancy in the nearest neighbour position. If the crystal contains a concentration of divalent cation impurity which is equal to or more than that of CrO₄^2? ions, a different spectrum characteristic of C_2x symmetry as well as the line corresponding to T_d symmetry are obtained. The crystals of ordinary purity contain all the three (C_s, C_2x and T_d symmetry) species and show eight line spectra. The changes in force constants calculated from the observed splitting of the energy levels agree with those evaluated from the known polarizability of the chromate ions.At 600°C, the vibration spectra of the highly pure crystals doped with CrO₄^2? ions show an increase in intensity of the line characteristic of T_d symmetry and the other lines practically disappear, because the anion vacancies move away from the neighbourhood of the CrO₄^2? ions at high temperatures. The energy of association of the vacancy with CrO₄^2? ions and the energy of migration of the vacancy are derived from the spectra obtained at different temperatures and with different heat treatments.The electronic spectra of the crystals show 3 bands (at 345, 270 and 240 nm for KCI). The lowest energy band has a fine structure with a spacing of about 800 cm^?1 at LAT. Since the transition involved is from a non-bonding to an antibonding state, the Condon parabola is shifted in the excited state and therefore the fine structure is attributed to a vibrational progression involving a totally symmetric frequency 800 cm^?1 in the excited state.