Cobalt oxide, photosensitizer

Photooxidafions are also iudustriaHy significant. A widely used treatment for removal of thiols from petroleum distillates is air iu the presence of sulfonated phthalocyanines (cobalt or vanadium complexes). Studies of this photoreaction (53) with the analogous ziuc phthalocyanine show a facile photooxidation of thiols, and the rate is enhanced further by cationic surfactants. For the perfume iudustry, rose oxide is produced iu low toimage quantifies by singlet oxygen oxidation of citroneUol (54). Rose bengal is the photosensitizer. 

The reaction of diethyl zinc with water produces zinc oxide, and then zinc carbonate, as the alkaline reserve. These chemicals have antiseptic properties which may also prevent the growth of mold in paper. They may also improve the brightness of treated papers. However, it is also known that zine oxide is a photosensitizer (56) which may trigger photo-oxidation of treated papers to initiate a chemical chain reaction that will lead eventually to the formation of acidic products (57). Moreover, the interaction of zinc oxide and zinc carbonate with copper, iron and cobalt present in the paper and their subsequent effects on paper stability have not been studied. 

Cobalt(III) cage complexes can also perform as electron transfer agents in the photoreduction of water. Because of the kinetic inertness of the encapsulated cobalt(II) ion, the cobalt(II)/co-balt(lll) redox couple can be repeatedly cycled without decomposition. Thus these complexes are potentially, useful electron transfer agents, e.g. in the photochemical reduction of water, in energy transfer and as relays in photosensitized electron transfer reactions. The problem of the short excited-state lifetimes of these complexes can be circumvented by the formation of Co(sep) ion pairs, so that the complexes can be used as photosensitizers for cyclic redox processes. Related ligands such as (51) have also been reported, and mixed N and S donor atoms have been used to isolate lower oxidation states, e.g. cobalt(I). ... 

Water and carbon dioxide do not absorb light above 200 nm and their monoelectronic reduction requires an energy too high to be performed by classical transition metal complexes. It is therefore necessary to use a photosensitizer and organometallic complexes which are able to transfer more than one electron (e.g. cobalt(I), ruthenium(O), or rhenium(-I) or iridium(I) complexes). In principle, these species could be oxidized to a higher oxidation state, by reaction with water or carbon dioxide. However this poses certain problems (i) the compatibility of redox potentials between the photosensitizer and the catalyst (ii) finding mediators and... 

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