Aromatic ketones as sensitizers

Benzophenone is the most important representative of this class of compound. A benzophenone molecule is excited by an absorbed light quantum to the triplet state [Refs. 60,116, 483, 624]. In the triplet state the spins of two electrons of the carbonyl group are parallel, which is similar to a biradical [257]. In the excited triplet state the unpaired electrons, however, belong to a definite energetic state of a molecule, whereas in a biradical they are ascribed to determined atoms or fragments of a molecule [399, 408, 409]. 

Pitts et al. [480] and Beckett and Porter [61, 62] found that benzophenone sensitizes the oxidation of isopropanol in accordance with the following reaction scheme. 

On the basis of the above mechanism Dulog et al. [192] proposed the following mechanism for the oxidation of polyvinyl alcohol in aqueous solutions by benzophenone-3,3 -disodium-disulphate, which is also soluble in water. 

Dulog et al. [192] also suggest an ionic mechanism for the decomposition of the hydroperoxide namely, 

The photoreduction of benzophenone in benzene has been investigated by many workers [Refs. 63,183, 481, 483]. Benzophenone in the lowest excited triplet state 3(n,n ) abstracts hydrogen from benzene, producing a ketyl and a phenyl radical  

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