Photochemical technology

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

Photochemical technology has been developed so as to increasingly exploit inorganic and organometaUic photochemistries (2,7), recognizing the importance of photoinduced electron transfer as the phenomenological basis of a majority of commercially successful photochemical technologies (5,8). 

Use of coherent light sources in industrial appHcations has led to the field of photodynamic therapy as a photochemically based medical technology (9—11). The apphcation of photochemistry to information storage and communication processes is expected (12) (see Information storage materials Resist materials). 

Conventional, incoherent light sources suitable for industrial-scale photochemistry and the reactors exploiting them have been reviewed in depth (2). Subsequent improvements in traditional light sources have been incremental. 

Previous expositions of photochemical laws have distinguished ptominentiy between states of singlet and triplet multiplicity (1). This distinction continues to be important with respect to photophysics of smaH organic molecules, but among inorganic and organometaHic compounds, states of other multiplicities, eg, doublet and quartet states (23), play an important role. Spin conservation characterizes electronic molecular excitations and localized 

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Subliming ablators are being used in a variety of manufacturing appHcations. The exposure of some organic polymers to pulsed uv-laser radiation results in spontaneous ablation by the sublimation of a controUed thickness of the material. This photoetching technique is utilized in the patterning of polymer films (40,41) (see PHOTOCHEMICAL TECHNOLOGY). 

The radicals are then involved in oxidations such as formation of ketones (qv) from alcohols. Similar reactions are finding value in treatment of waste streams to reduce total oxidizable carbon and thus its chemical oxygen demand. These reactions normally are conducted in aqueous acid medium at pH 1—4 to minimize the catalytic decomposition of the hydrogen peroxide. More information on metal and metal oxide-catalyzed oxidation reactions (Milas oxidations) is available (4-7) (see also Photochemical technology, photocatalysis). 

Photochemical technology Photoconductive polymers Photography Printing processes Radioactive tracers Radiopaques... 

Laser Photochemistry. Photochemical appHcations of lasers generally employ tunable lasers which can be tuned to a specific absorption resonance of an atom or molecule (see Photochemical technology). Examples include the tunable dye laser in the ultraviolet, visible, and near-infrared portions of the spectmm the titanium-doped sapphire, Tfsapphire, laser in the visible and near infrared optical parametric oscillators in the visible and infrared and Line-tunable carbon dioxide lasers, which can be tuned with a wavelength-selective element to any of a large number of closely spaced lines in the infrared near 10 ]lni. 

CycIoa.ddltlons. Cyclobutene adducts are formed from the reaction of acetylenic derivatives and maleic anhydride through a 2 + 2 cycloaddition (48). The reaction is photochemicaHy cataly2ed (see Photochemical technology). 

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