Photochemistry of diaryliodonium salts

Photochemistry of Diaryliodonium Salts. The photochemistry of diaryliodonium salts having nucleophilic anions is illustrated... 

Dektar and Hacker report on the photochemistry of diaryliodonium salts in the case of direct photolysis and in the case of energy transfer from a photosensitizer [26], The photoproducts and the reaction mechanisms are different in the two situations (Scheme 12.5). 

SCHEME 12.5 Proposed photochemistry of diaryliodonium salts in the case of direct photolysis. 

Diaryliodonium salts are widely used as photoinitiators for cationic photopolymerizations [17-20]. Photoini-tiated cationic polymerization is of great practical interest due to its applicability for the curing of coatings and printing inks and for photoresist technology used in lithography [19,20]. General synthetic methods, properties and photochemistry of diaryliodonium salts as photoinitiators were reviewed by Crivello in 1984 [18]. 

Photochemistry of Diaryliodonium Salts and Related lodonium Salts... 

The photochemistry of diaryliodonium salts has been investigated extensively for use in cationic polymerization and microlithographic applications (chemical amplification).In principle, these applications are based on the generation of a strong acid by the photolysis as shown in Scheme 1. 

J.P. Fouassier, D. Burr, and J.V. Crivello, Photochemistry and photopolymerization activity of diaryliodonium salts. J. Macromol. Sci. Pure Appl. Chem. 1994, A31(6), 677-701. 

The major portion of the article will be devoted to a discussion of the synthesis and mechanistic aspects of photoinitiation by individual photoinitiator systems. Cationic polymerizations induced by these photoinitiators are dark, i.e., non-photo-chemical, processes which are governed by the same parameters which must be taken into account in polymerizations which occur in the presence of conventional initiators such as Lewis and Bronsted acids. Accordingly, cationic polymerizations induced by halogen and sulfur based onium salt photoinitiators will be discussed only from the context in which they are influenced by factors which have their origin in the photoinitiator. Since the photochemistry of diaryliodonium and triarylsulfonium salts is similar, these two types of photoinitiators will be discussed together. The photolysis of dialkylphenacylsulfonium and dialkyl-4-hydroxyphenylsulfonium salts proceeds by a different mechanism, and they will be discussed separately. 

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