Photoreaction and photopolymerization studies on squaraine dyes/iodonium salts combination

A novel visible photosensitized system, squaraine dye (SQ)/iodonium salt (On) combination, used as a radical photogeneration source has been suggested and studied. The thermodynamic data and experimental results show that the SQ/On combination readily undergoes photoreaction via fast intramolecular ion-pair electron transfer within the short time scale of excited lifetime of SQ, simultaneously resulting in a photobleaching of SQ dye and a generation of active radical species released by subsequent decomposition of onium product. Some important factors that affect the formation of ion-pair complex between SQ dye and onium salts, such as solvent polarity, nature of counter anion, concentration of SQ dye and onium salt, show a large influence on the photoreaction kinetics. Based on the results of primary photoreaction, the visible photopolymerization using SQ/On combination as photoinitiator was studied in the solution and film. The synchronous photopolymerization and photobleaching behaviors were found in the polymerization process. The dye-sensitized photoreaction mechanism of SQ/On system was also proposed and discussed.