Journal of Photochemistry最新文献

o-Nitrobenzyl benzoate (oNBB), α-methyl-o-nitrobenzyl benzoate (αMoNBB), α-phenyl-o-nitrobenzyl benzoate (αPoNBB) and copolymers of methyl methacrylate and of o-nitrobenzyl, methyl-o-nitrobenzyl and phenyl-o-nitrobenzyl acrylates were flash photolysed or continuously irradiated with UV light in dilute solution. The quantum yield φ(PR) of bond cleavage in the photorearrangement of the o-nitrobenzyl esters does not depend on the chemical nature of the ester group but is significantly influenced by the substituent in the α position φ(PR) = 0.22 ± 0.03 (αMoNBB, αPoNBB) and φ = 0.10 ± 0.02 (oNBB). This was revealed from the yields of carboxylic acid and o-nitrobenzyl groups. The differences in φ(PR) correspond to the differences in the yields of nitronic acid formed as an intermediate. In aqueous systems the kinetics of the decay of the nitronic acid were found to be determined by the formation of rather stable nitronate ions according to the equilibrium

The main purpose of this paper is to apply the density matrix formalism for treating multiphoton ionization of multirovibronic level systems. Both direct photoionization and photoionization through autoionization states are taken into account. Numerical results will be presented for demonstrating the effect of the interference resulting from the neighboring rovibronic levels. The theoretical results are applied to interpret two sets of experimental data on two-color photoionization of molecules; one set is for two-color threshold photoionization spectra of jet-cooled aniline which exhibit autoionizing Rydberg structures and the other is for high resolution Rydberg spectra of H₂ by stepwise resonance two-photon ion-pair (H⁺ + H⁻) production.

ϵ(Poly(l-lysine) containing a high mole percentage of azo aromatic side chains was synthesized by the active ester method. The photochemical properties of the azo polypeptide, ϵ-poly(N^α-phenylazobenzoyl-l-lysine) (ϵ-PPABLL), were investigated by absorption and circular dichroism (CD) spectroscopy in hexafluoro-2-propanol (HFIP). The photochromism of the absorption band in the near UV and visible wavelength region was found to be mostly reversible as a function of irradiation time at different wavelengths (360 nm and 460 nm) owing to the trans—cis photoisomerization of the azo aromatic moieties. The CD spectrum exhibited multistage photochromism on irradiation by light. The whole CD spectrum, especially at the dichroic bands at 300 nm (positive), 340 nm (negative) and 365 nm (trans, positive), showed a peculiar reversible photochromism on irradiation by 360 nm and 460 nm light, except the first irradiation time course. The position and magnitude of the negative dichroic band at 225 nm suggested that the backbone conformational change of ϵ-PPABLL was a light-induced partial reversible transition from a β-form-rich structure to a random-coil-rich structure.

The dechlorination of 4-chlorobiphenyl (ClBi) photosensitized by N,N-dimenthylaniline (DMA) was studied in methanolic and ethyl acetate solutions by means of continuous photolysis at 313 nm. The hydrogen chloride quantum yield was measured as a function of ClBi concentration. The reaction proceeds mainly via DMA singlet state sensitization.

Excited singlet deactivation of DMA by ClBi was investigated by fluorescence quenching. In low polarity solvents such as cyclohexane and ethyl acetate, the fluorescence quenching was accompanied by the appearance of the fluorescence band of an exciplex. The fluorescence quenching of the DMAClBi exciplex by tetrabutylammonium perchlorate and lithium perchlorate was also studied. Both salts enhanced the sensitized dechlorination of ClBi and an electrostatic interaction between undissociated perchlorates and the exciplexes is postulated to be responsible for the enhanced dechlorination.

We have investigated the fluorescence and phosphorescence spectra of harmol and harmalol in the solid phase at 77 K. Three molecular species, namely, the cation, the neutral molecule and the molecular anion are characterized for harmol in both the fluorescence and phosphorescence spectra. We have also identified three molecular species, namely, the cation, the zwitterion and the molecular anion in the fluorescence spectra of harmalol but only the cation and the molecular anion in the phosphorescence spectra.

The excited state pK_a values in the first excited triplet state T₁ have been estimated from the Förster equation. It is found that in the first excited triplet state the ring nitrogen atom is more basic and the hydroxy group is more acidic than in the ground state.

The methylene-blue-sensitized hydroxylation of 2-hydroxybenzoic acid by hydrogen peroxide initiated by visible radiation and catalysed by ferric chloride has been investigated. The major reaction product is 2,3-dihydroxy-benzoic acid. In the absence of iron(III), the reaction occurs extremely slowly. Iron(III) is observed to have an appreciable catalytic effect on the photosensitized reaction at concentrations as low as 10⁻⁸ M. The first step of the reaction is the photochemical reduction of iron(III) to iron(II), i.e. the generation of Fenton's reagent.

The photochemical reduction of uranyl ions by triphenylphosphine, tri-p-tolylphosphine, triphenylarsine and tri-p-tolylarsine in a dry acetone medium in the presence of trimethylacetic acid, using radiation in the visible region (λ > 365 nm), was investigated. The electron spin resonance and electronic spectral data supported the proposal that uranium(V) was formed. The quantum yields and Stern—Volmer quenching constants were also calculated for all four types of substrate. Keeping in view the available evidence, an electron transfer mechanism was postulated for the formation of uranium(V) which disproportionates into uranium(IV) and uranium(VI) in aqueous acidic media.