Photosensitization experiments

Another class of carbonyl compounds that has received much attention is the cyclohexadienones. The primary photolysis product of 4,4-diphenylcyclohexadienone, for example, is 5. Quenching and photosensitization experiments have indicated that the... 

The fact that dimers (10)—(12), produced in the direct photolysis of butadiene, were not observed in the photosensitized experiments may indicate that these are derived from the excited singlet state of butadiene/ ... 

We shall discuss now the redox properties of the dye molecule rhodamine which is often used in photosensitization experiments. 

The original substrate structure used for our early photosensitization experiments was a fractal surface derived by hydrolysis of an organo-titanium compound, but this has since been replaced with a nanostructured layer deposited from a colloidal suspension of TiOi. This evidently provides for a much more reproducible and controlled high-surface-area nanotexture. Further, because it... 

In the photosensitized experiments, the cellulose sample was treated with a solution of the initiator in acetone for 1 h at room temperature and the solvent evaporated in air. When this kind of adsorption was not possible, the initiator was dissolved in THF and added to the reactant medium. 

As reported in literature (13) the irradiation of a cellulose sample at 254 nm results in glucosidic bond scission and C - H bond scission. Recent results in photosensitized experiments (15) show that the same behaviour can be obtained ... 

In liquid phase photosensitization experiment it was observed that triplet photo-sensitizers (benzene, benzophenone), in spite of efficient energy transfer to azo-... 

O-methyl oxime ether of 2-acetonaphthone has also been reported to undergo facile syn -> anti photoisomerization.6 The composition of the photostationary state appears to be concentration-dependent with the sy/i-isomer predominating at low concentrations. Evidence supporting the involvement of the singlet state was obtained from fluorescence-quenching studies and from photosensitization experiments. 

Direct interaction of the excited state with a chiral environment seems the most attractive way to create asymmetry in photoproducts, because the chiral inductor is not destroyed during the reaction. Since the pioneering work on the asymmetric isomerization of cyclopropanes in photosensitized experiments [12] was published, recent reports have shown that high selectivities can be achieved in asymmetric photosensitizations [13]. However, the most promising results for synthetic applications involve photoreactions in rigid and organized media such as chiral monocrystals or inclusion complexes. 

The photoisomerization of acyclic alkenes is well documented in both the direct and the photosensitized experiments (79). Of course, the cis-trans process does not need to be discussed here see above and (58). Let us only recall that in direct photochemistry it has been linked to the skew structure of the ( ir,ir ) excited state (80). The internal methyl shift was attributed to the Rydberg [ rr,R(3s)] electronic state. This process is particularly efficient in the gaseous and liquid phase photoirradiation of tetramethylethylene (81-83) ... 

Quenching and photosensitization experiments on representative examples have indicated that the reaction proceeds through a triplet excited state. A scheme that delineates the bonding changes is outlined below ... 

Light can profoundly affect in vivo and in vitro toxin bioassays, as has been documented by photosensitization experiments using livestock and poultry (Towers 1980 Ivie 1982). Photoactivation of quinones, certain alkaloids, and other compounds can be assessed by, for example, exposure of agar plates used in diffusion assays to UV-A light (320-400 nm, 5 W/m ) for 2 h while keeping control plates in the dark (Taylor et al. 1995). 

The electrochemical and photosensitization experiments performed on the A-type and B-type dendrimers have evidenced that (Tables 4.1 and 4.2) in all cases only a... 

Energy transfer to 2,3-butanedione from 2-butanone excited at 313 nm was studied by Lissi et al. (1973/1974) through observed phosphorescence of 2,3-butanedione triplets. They found that the quantum yield of triplet 2-butanone formation was near unity at high pressures (400 Torr) of added propane. The triplet lifetime was reported to be 1.3 X 10 and 1.8 x 10 s at 400 and 14Torr, respectively. They reported co = 0.9 at 120°C, 100 Torr pressure, and low light intensity. From 2,3-butanedione photosensitized experiments, the rate coefficient for the photocleavage of 2-butanone triplet (400 Torr total pressure) as estimated by Abuin and Lissi (1975) is represented by the function ... 

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