Organic photoproducts

Indirect evidence of organic photoproduct generation comes from structural analyses of DOM. Several reports have used NMR in the solid and solution... 

A photoreaction that has been studied extensively by Satos [41] group is the oxidation of cycloalkenes in the presence of FeCL and oxygen to yield, depending on the substrate, a-chloro- or o)-dichloroketones. Scheme 15. Since the chloride ion is incorporated into the organic photoproduct the reaction as it was conducted is not catalytic but requires stoichiometric... 

In this system, the aqueous photoproduct, [Ru(bpy)3] ", is more hydrophilic than the aqueous reactant, [Rulbpyls], and the organic photoproduct, C7V , is more hydrophobic than the organic reactant, C7V ", guaranteeing that the photocurrent observed was purely electronic. Other systems, using [Ru(bpy)3] + as the photosensitiser in the aqueous phase and TCNQ [tetracyanoquinodimethane] as a reversible organic quencher, have recently been studied and shown to be able to act as photoelectrical energy converters. 

A more workable photopolymer system was based on the chemistry of diazonium salts. The diazo salt or diazo resin can be coated from water along with a water soluble binder, such as poly (vinyl alcohol). Upon exposure the salt is photolyzed, probably forming a phenol or haloaro-matic. The neutral organic photoproducts dissolve much more slowly than do the ionic starting materials. 

At present, several stable photocatalytic systems for production of hydrogen from water and organic compounds are made of semiconducting oxides and suitable proton reducing catalyzer. An efficient electron transfer between inorganic semiconductor and bacterial hydrogenase was shown to result in hydrogen photoproduction. 

Zepp RG, Braun AM, Hoigne J, et al. 1987. Photoproduction of hydrated electrons from natural organic solutes in aquatic environments. Environ Sci Technol 21 485-490. 

Ormerod, J.G., Ormerod, K.S., Gest. H. 1961. Light-dependent utilization of organic compounds and photoproduction of molecular hydrogen by photosynthetic bacteria relationships with nitrogen metabolism. Arch Biochem Biophys 94 449 63. 

Larson et al. (1992) studied the photosensitizing ability of 2, 3, 4, 5 -tetraacetylriboflavin to various organic compounds. An aqueous solution containing aniline was subjected to a medium-pressure mercury arc lamp (X >290 nm). The investigators reported that 2, 3, 4, 5 -tetraacetylribofiavin was superior to another photosensitizer, namely riboflavin, in degrading aniline. Direct photolysis of aniline without any photosensitizer present resulted in a half-life of 23 h. In the presence of riboflavin and 2, 3, 4, 5 -tetraacetylribofiavin, the half-lives were 1 min and 45 sec, respectively. Photoproducts identified in both reactions were azobenzene, phenazine, and azoxybenzene. 

Major photoproducts reported in soil treated with alachlor were 2, 6 -diethylacetanilide, 1-chloro-2, 6 -diethylacetanilide, 2,6-diethylaniline, chloroacetic acid, 2, 6 -diethyl-A -methoxy-methylaniline, and l-chloroacetyl-2,3-dihydro-7-ethylindole. Organic matter in soil enhanced the rate of photolysis (Chesters et al, 1989). 

The photoactive compounds, or sensitizers, that are used in the formulation of positive photoresists, are substituted diazonaphthoquinones shown in Figure 17. The substituent, shown as R in Figure 17, is generally an aryl sulfonate. The nature of the substituent influences the solubility characteristics of the sensitizer molecule and also influences the absorption characteristics of the chromophor (79). The diazonaphthoquinone sulfonates are soluble in common organic solvents but are insoluble in aqueous base. Upon exposure to light, these substances undergo a series of reactions that culminate in the formation of an indene carboxylic acid as depicted in Figure 17. The photoproduct, unlike its precursor, is extremely soluble in aqueous base by virtue of the carboxylic acid functionality. 

Photoinduced electron transfer (PET) has attracted considerable interest and has been intensively studied as a fundamental step in mechanistic and synthetic organic photochemistry and appears to be involved in key biological processes. Cyclore version of oxetans by PET is important for the photoenzymatic repair of the photoproducts of the DNA dipyrimidine sites by photolyase244. The oxidative version of this reaction has been achieved using cyanoaromatics, chloranil, or (thia)pyrylium salts as electron-transfer photosensitizers245 246. 

DellaGreca, M., Iesce, M.R., Isidori, M., Montanaro, S., Previtera, L. and Rubino, M. (2007) Phototransformation of amlodipine in aqueous solution toxicity of the drug and its photoproduct on aquatic organisms, bit. J. Photoenergy, article ID 63459. 

Isidori, M., Nardelli, A., Pascarella, L., Rubino, M. and Parrella, A. (2007) Toxic and genotoxic impact of fibrates and their photoproducts on non-target organisms. Environ. Int., 33 (5), 635-641. 

Intramolecular hydrogen-transfer to an excited imine is responsible for the photochromism of derivatives of salicylaldehyde (o-hydroxybenzaldehyde) irradiation converts the colourless or yellow imine into a much more intensely coloured photoproduct 15.9), but removal of the light source allows rapid reversal of the process. Reactions of this kind form the basis of some organic photochromic glass formulations exposure to increasingly bright light alters the proportion of the isomers in favour of the dark-coloured photoproduct. 

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