Photochemical technology applications

The progress achieved in the detailed understanding of photophysical and photochemical processes that may be induced by light-irradiation in particular spin crossover systems has driven research efforts towards the development of materials that may be used for various technological applications. Only relatively recently, reports have appeared exploring this field for Fe(III) spin crossover materials. 

Organic solids have received much attention in the last 10 to 15 years especially because of possible technological applications. Typically important aspects of these solids are superconductivity (of quasi one-dimensional materials), photoconducting properties in relation to commercial photocopying processes and photochemical transformations in the solid state. In organic solids formed by nonpolar molecules, cohesion in the solid state is mainly due to van der Waals forces. Because of the relatively weak nature of the cohesive forces, organic crystals as a class are soft and low melting. Nonpolar aliphatic hydrocarbons tend to crystallize in approximately close-packed structures because of the nondirectional character of van der Waals forces. Methane above 22 K, for example, crystallizes in a cubic close-packed structure where the molecules exhibit considerable rotation. The intermolecular C—C distance is 4.1 A, similar to the van der Waals bonds present in krypton (3.82 A) and xenon (4.0 A). Such close-packed structures are not found in molecular crystals of polar molecules. 

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

Like many of the topics discussed in this book, photochemical reactions are most likely to be used in niche applications for commercial and environmental reasons. Unless there is a major breakthrough in reactor and lamp design, widespread use of this technology is unlikely. Perhaps the best hope of producing high-intensity monochromatic sources of radiation rests with lasers, but currently equipment costs are too high to justify their use for commercial chemical production. 

Eheich, H., Linke, D., Moegen-scHWEis, K., Baerns, M., Jahnisch, K., Application of microstructured reactor technology for the photochemical... 

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