Cationic photoinitiators. Acid generation from the photodecomposition of triphenylsulfonium and triphenylselenonium salts

Abstract

Direct photolysis of triphenylsulfonium salts and triphenylselenonium salts gives in-cage recombination products and cage-escape products. Acid is generated from each of these processes. The detection of acetanilide or anisole, and the meta-isomer of the recombination products implies the intermediacy of phenyl cation from photolysis of sulfonium and selenonium salts. Phenyl radical is also an intermediate and reacts with solvent to give benzene and with diphenylsulfinyl radical cation to give the ortho- and para-recombination products and acid. These intermediates give strong evidence for both heterolytic and homolytic cleavage pathways from photolysis of both sulfonium and selenonium salts. The cage: escape ratio and quantum yields for product formation are dramatically affected by solvent viscosity. Triplet sensitization of sulfonium salts gives exclusively escape products, whereas some recombination reaction is observed from triplet sensitization of selenonium salts.