Diaryliodonium salt photolysis quantum yield

Abstraction of labile hydrogen atoms, for example, from tetrahydrofuran (THF), by photoexcited ketones also yields easily oxidized radicals [60a]. Quantum yields for benzophenone sensitized photolysis of diphenyliodo-nium hexafluoroarsenate in acetonitrile with hydrogen atom donors are shown in Table 9. Diaryliodonium salts are capable of oxidizing electron rich radicals from isopropanol and THF but triarylsulfonium salts are not [96]. The oxidation potential of tetrahydrofuranyl radical is —0.35 V versus SCE [109], apparently sufficient for irreversible reduction of diphenyliodonium cation ( red = approx. —0.7 V versus SCE, see above) but not of triphenyl-sulfonium cation ( red = —1.2V versus SCE). 

In most respects, diaryliodonium salts are nearly ideal as cationic photoinitiators for the ring-opening polymerizations of heterocyclic monomers. The photolysis of diaryliodonium salts is highly efficient with quantum yields of the order of 0.7 based on the amount of acid generated. Not only are they... 

In contrast to the photolysis of diaryliodonium salts in acetonitrile which gives quantum yields for the formation of aryliodides of < 1, photolysis in tetrahydrofuran (THF) at 366 nm gives quantum yields of approximetaly Quantum yields greater than unity in this case suggest that a chain induced decomposition of the... 

In all cases, these photoinitiators were less efficient than diaryliodonium and triaryl-sulfonium salts under comparable conditions. To date, there has been no report of a study of the mechanism of photolysis of these compounds nor have the quantum yields been determined. Since thiopyrylium salts are colored compounds, they may be useful photoinitiators in the visible region of the spectrum. The related thio-xanthylium salts were also examined as potential photoinitiators but were too hydrolytically unstable to be useful... 

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