Search results for "Photochemistry"

High atomic yield bromine-less benzylic bromination

2002

A two-phase mixture (sodium bromide, aqueous hydrogen peroxide/carbon tetrachloride or chloroform) under visible light provides a simple and convenient system for benzylic bromination of toluenes. A high atomic yield for bromine atoms is attained. Substitution of the chlorinated solvents by other more environmentally benign organic solvents has been attempted and good results are obtained for methyl pivalate.

Photophysics and photostability of adenine in aqueous solution: A theoretical study

2010

Abstract The sequential Monte Carlo/CASPT2 approach was employed to investigate deactivation and emission processes from the lowest-lying ππ∗ and n π∗ excited states of 9H-adenine in aqueous solution. It is found that conical intersections connecting the ππ∗ and n π∗ states with the ground state are also present in solution, whereas the barriers for the deactivation paths are significantly smaller on solvated conditions. The large destabilization of the n π∗ state found in solution possibly prevents its involvement in the deactivation photophysics and explains the change from a bi- to a mono-exponential decay for the molecule in the gas phase and solution, respectively.

Polyamine Linear Chains Bearing Two Identical Terminal Aromatic Units. Evidence for a Photo Induced Bending Movement

2001

Abstract Several chemosensors bearing a fluorescent unit at both ends of a linear polyamine chain were synthesised. The protonation as well as the association constants with Cu2+ and Zn2+ were determined by potentiometry in 0.15 mol dm−3 NaCl at 298.1 K. In the case of 1,16-bis(1-naphthylmethyl)-1,4,7,10,13,16-hexaazadecane hexahydrochloride (L1), formation of an excimer emission in aqueous acidic solutions was observed. The system was characterized by steady state fluorescence emission and by time resolved fluorescence. In the ground state the molecule is expected to adopt a more or less linear conformation, while in the excited state a bending movement of the chain must occur in order to …

Polychromatic femtosecond fluorescence studies of metal–polypyridine complexes in solution

2011

Femtosecond-resolved broadband fluorescence studies are reported for[ M(bpy)(3)](2+) (M = Fe, Ru), RuN3 and RuN719 complexes in solution. We investigated the pump wavelength dependence of the fluorescence of aqueous [ Fe(bpy)(3)](2+) and the solvent and ligand dependence of the fluorescence of Ru-complexes excited at 400 nm. For all complexes, the (MLCT)-M-1 fluorescence appears at zero time delay with a mirror-like image with respect to the absorption. It decays in <= 30-45 fs due to intersystem crossing to the (MLCT)-M-3 states, but a longer lived component of similar to 190 fs additionally shows up in RuN719 and RuN3. No solvent effects are detected. The very early dynamics are character…

Hole Localization and Thermochemistry of Oxidative Dehydrogenation of Aqueous Rutile TiO2(110)

2012

The photochemical rearrangement of polymeric N-(1-pyridinio) amidates. A novel, aqueous photoresist system

1988

Spectral studies of zinc octacarboxyphthalocyanine aggregation

2009

The association of zinc octacarboxyphthalocyanine, was studied using UV–vis absorption and fluorescence emission spectroscopy; the effects of dye concentration, pH and solvents on spectra were discussed. Calculations showed that the dye dimerized in aqueous solutions ranging from 5.0 × 10−7 to 5.0 × 10−5 mol/dm3, at 25 °C. The dimerization constant of 106 dm3/mol and the spectral Q band shift of 1185 cm−1 imparted by dimerization indicated strong π–π interactions between phthalocyanine molecules. Red S1 fluorescence of the dye monomer was observed in various solutions which was quenched owing to molecular association and other factors. The strong influence of pH on both aggregation and fluo…

Photocatalytic Oxidation of Cyanides in Aqueous Titanium Dioxide Suspensions

1997

The photocatalytic oxidation of free cyanides in aqueous suspensions containing polycrystalline TiO2(anatase) powders irradiated in the near-UV region has been investigated. The rate of cyanide photooxidation has been studied by varying the following operative parameters: (i) initial cyanide concentration; (ii) catalyst concentration; (iii) initial pH; (iv) power of irradiation; and (v) chloride ion concentration in the reacting mixture. Under the used experimental conditions the photoreaction proceeded at a measurable rate until the complete disappearance of cyanides. The kinetics of cyanide photooxidation is affected by the catalyst concentration, the chloride ion concentration, and the p…

Complexes of tetra(parasulphonatephenyl)porphyrinato ferrate(III), FeTPPs, with 1,10 phenanthroline and 2,2′ bipyridine ligands

1985

Abstract Iron(III) porphyrin, FeTPPS, gives high-spin 1:1 monomeric complexes with the ligands 1,10 phenanthroline, 2,9 dimethylphenanthroline and 2,2 bipyridine in aqueous solution. Absorption spectrum of the complexes is very different to the one of the monomer metalloporphyrin, but nearly identical to the visible spectrum of the μ-oxo dimer Fe2(TPPS)2O. A spectrophotometric study of the formation equilibria yields the following values of the stability constants: Me2phen 4.3 × 104, phen 1.1 × 104, bipy 2.0 × 102 (25 °C, 0.1 M NaNO3). Analysis of the experimental data strongly suggest that the ligands are hydrogen bonded to one coordinated water molecule (TPPS)FeOH2 → (LL). Although the …

Photocatalytic oxidation of toluene on irradiated TiO2: comparison of degradation performance in humidified air, in water and in water containing a z…

2003

Photocatalytic degradation of toluene was carried out both in gas–solid and in liquid–solid regime by using polycrystalline samples of TiO2 Merck and TiO2 Degussa P25. For the gas–solid regime two types of continuous photoreactor were used, a fixed bed one of cylindrical shape and a Carberry type photoreactor, both irradiated by near-UV light. The inlet reacting mixture consisted of air containing toluene and water vapours. The influence of the gas flow rate and the presence of water vapour on the photocatalytic process was investigated. CO2 and benzaldehyde were the toluene degradation products detected in the gas phase by using TiO2 Merck. In the presence of water vapour this catalyst exh…