Photolabile compound

The color of the vial wall may also be of importance when photolabile compounds are analyzed. In these circumstances, brown vials are generally used, although in some special cases, green, blue, or red vials may be more appropriate. However, the dyes in the colored vials may sometimes interfere with the analysis. In such cases, transparent vials should be used photodegradation of the samples can also be avoided by wrapping the vials in aluminum foil. 

Table 2 lists atmospheric lifetimes for a range of anthropogenic molecules. As seen from Table 2 the lifetimes of pollutant molecules range from minutes or hours for photolabile compounds such as CF3I and HCHO to millennia for perfluoro compounds such as CP4 and SF6. There is discussion as to whether... 

Table 6.6 lists the most important phototransformations discussed in this section. The carbonyl compounds (entries 1 6) are typical representatives of the photolabile compounds. Their reactions played an essential role in revealing the mechanisms of some primary photochemical steps. Thanks to their excellent absorption properties, thermal stability, usually uncomplicated synthesis and reaction diversity, they represent popular starting material in applied synthetic or material photochemistry and in photobiochemistry. It is... 

The first step for the development of polymers sensitive to 308-nm irradiation was the designing of various photolabile compounds for physical doping (solvent mixing) of polymers [117, 118]. The best results have been achieved by using triazene (-N=N-N-) or pentazadiene compounds (-N=N-N(R)-N=N-). The n-n transition of the -N=N-X- chromophore is located around 300 nm [119]. 

Mode of action. PPIX is a photolabile compound, so the question of whether sufficient levels of it can exist in vivo for it to exert its effect is important. We found the half-life of PPIX in acifluorfen-treated cucumber tissue during exposure to bright light to be about 2.5 h (41) - sufficient time for it to be an effective herbicide. Furthermore, PPIX accumulated rapidly in bright light and did not begin to decrease until cellular damage was nearly complete. 

Forward and reversed optics are also discussed in terms of influence on sample stability. Reversed optics increases the probability of decomposition of photolabile compounds, because the whole wavelength range is passed through the sample. These are by no means conclusive results, as it is difficult to compare effects of a single full wavelength fast exposure of the sample (produced with a reversed optics instrument) with those of a cumulative long-term exposure made by a scanning instrument. Both examples of induced sample decomposition as well as successful analysis of well-known photosensitive compovmds by means of diode array instrumentation have been reported in the literature. 

The photoinitiator makes the resin formulation UV-curable. Only the development of thermally stable but photolabile compounds enabled the development of UV curing. For an efficient UV curing, the absorption of the photoinitiator should match, at least partly, the emission spectrum of the light source used. Two main types of photoinitiators are used photoinitiators based on an a-deavage process (Norrish type I), and photoinitiators based on an electron transfer followed by a hydrogen abstraction process (Norrish type II). a-Cleavage photoinitiators are mono-molecular initiators, of which a-hydroxy or a-alkoxy ketones and benzoyl phosphine oxides are well known examples shown in Scheme 16.33. 

The most common initiating agents used in the preparation of MIPs are azo compounds like the frequently used N-N -bis isobutyronitrile (AIBN) and 2,2 -azobis-(2,4-dimethylvaleronitrile) peroxo compounds like hydroperoxides, dialkyl peroxides, diacylperoxides and peresters oxidation-reduction systems like organic/inorganic peroxide redox couples and low valency metallic or nonmetallic compoxmds as well as photolabile compounds with the tendency to absorb light, either directly or as a result of the presence of a photosensitizer [5]. 

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