Journal of Photochemistry最新文献

The changes induced in the structure of micelles of sodium dodecylsulphate when alkanes, alcohols and ketones are solubilized were studied by steady state fluorescence probing methods. Important information concerning micellar properties, such as size, micropolarity, interfacial charge density etc., obtained from fluorescence measurements are presented and some general trends are discussed.

The photodehydrocyclization of several mono-para-substituted 1,2-diphenylcyclopentenes into a phenanthrene derivative has been investigated under several conditions. It was found that the relative quantum yield of phenanthrene formation in methanol depends on the substituent when an oxidant with low efficiency (e.g. atmospheric oxygen) is used. In cyclohexane solution or in the presence of a more efficient oxidant, no significant substituent influence was observed. Furthermore, it has been established that the thermal ring opening of the primary photocyclization product dihydrophenanthrene (DHP) is influenced by substituents: an isokinetic relationship was found for this reaction but a linear Hammett relation was not observed. From these results it was concluded that the primary photocyclization step is not influenced by substituents. The quantum yield of product formation is influenced under conditions where thermal ring opening and oxidation of the intermediate DHP become competitive reactions (i.e. at low oxidation rates). The differences between the photocyclization behaviours of 1,2-diphenylcyclopentenes and stilbenes are discussed.

The fluorescence of 1,3-diphenylallyl lithium (DPALi⁺) in 2-methyltetrahydrofuran (MTHF) is due to the presence of the loose ion pair having the trans,trans conformation: no fluorescence from the cis,trans conformer could be detected. Conformational photoisomerization accompanies fluorescence. The lifetime and the quantum yield of fluorescence increase with decreasing temperature and reach limiting values by about −100 °C. A mechanism in which the excited state is deactivated by fluorescence and non-radiative decay in competition with activated twisting about the allylic skeleton is proposed and shown to be compatible with the observed temperature dependences. Alternative mechanisms involving the corresponding allylic radical are discussed.

The photo-oxidation of CH₂O in excess O₂ was studied at 253.7, 280.3, 312.8 and 326.1 nm at 25 °C. At all wavelengths except 253.7 nm, Φ(CO) = 1.0. At 253.7 nm, Φ(CO) = 0.77. The molecular photodecomposition is given by Φ(H₂), which is 0.28, 0.28, 0.16 and 0.40 respectively at the four wavelengths.

The radical scavenging effect of NO, in the system of C₂H₅Br photolyses in the vacuum UV region, has been studied as a function of the energy content of C₂H₅ radicals and of the irradiation time.

C₂H₆, one of the principal reaction products, from the primary radical process in the system can be completely suppressed by adding the appropriate amount of a radical scavenger, e.g. NO at greater than 0.1 Torr. However, by adding an unsuitable amount of NO, e.g. 0.02 Torr of NO and 50 Torr of C₂H₅Br, the reaction between the C₂H₅ radical and NO becomes competitive with that of the C₂H₅ radical and C₂H₅Br by the following mechanism:

The competitive reaction ratio between the C₂H₅Br/C₂H₅ and NO/C₂H₅ systems was obtained as a function of the irradiation energies with the variation in irradiation time by observing the production of C₂H₆. The values of k_NO^I/k₁, deduced by comparing the observed and the theoretical values, were found to be 4.0 × 10³ at 121.6 nm, 9.5 × 10³ at 147 nm, 14.0 × 10³ at 163.3 nm, 17.0 × 10³ at 174.3 – 174.5 nm and 23.0 × 10³ at 193.1 nm.

Electron transfer reactions occur between the triplet state of methylene blue and some terpenes, e.g. citronellol, α-pinene and β-pinene. The rate constants k_ET for these reactions were determined but no linear correlation between ln k_ET and the ionization potentials of the terpenes was found. This finding was explained in terms of stereoelectronic effects associated with the terpenes.