1,3-Bis(p-bromophenylamino)squaraine which functions as an electron-transfer photosensitizer for a wide range of diphenyliodonium salts radical photoinitiators of triacrylate polymerization under UV-blue light irradiation is presented. The functionality of the photosensitizer is determined by the presence of a suitable co-initiator. For this purpose, several different diphenyliodonium salts were used as a source of active species for radical polymerization. The reactivity of the new iodonium salts was studied with ultraviolet-blue light initiated radical polymerization by photo-DSC using squaraine dye as a sensitizer. The iodonium salts functionated as radical initiators bearing different substitution patterns. Electron transfer from the excited state of the sensitizer to the iodonium salt results in initiating radicals. The ability to initiate free radical polymerization of TMPTA by iodonium salts studied is similar. Most of the iodonium salts exhibit no large differences regarding the reactivity in initiation of TMPTA polymerization. However, an introduction of a nitro group in the para position of the phenyl ring of the co-initiator results in a significant increase in the rate of polymerization and degree of monomer conversion. The dye-sensitized photoreaction mechanism of the SQ/I system was also confirmed.

2-Ethyl-2-(hydroxymethyl)-1,3-propanediol triacrylate was polymerized in the presence of squarylium dye and various onium salts. The onium salts under study are commercially available or may be easily synthesized and are characterized by light absorption properties below 300 nm and generate phenyl radicals upon blue light exposure. Due to these interesting properties the triacrylate polymerization can be efficiently carried out with or without the presence of any additional photoinitiator. The chemical mechanisms are investigated by steady state photolysis and nanosecond laser flash photolysis experiments. The new photoinitiators yielded a higher visible light photoinitiating polymerization effect than the commercial photoinitiator: camphorquinone/ethyl p-(dimethylamino)benzoate and camphorquinone/N-methyldiethanolamine under experimental conditions.