Visible light-induced cationic photopolymerization by diphenyliodonium hexafluorophosphate and benzothiadiazole dyes

New benzothiadiazole-based long-wavelength organic dyes ( Y-1 and Y-2 ) were prepared for effectively sensitizing diphenyliodonium hexafluorophosphate (IOPF) to initiate the fast curing of bisphenol-A epoxy resin (E51) under visible light, avoiding traditional UV light sources that have high energy and high radiation. Y-1 and Y-2 have absorption spectra extended to more than 550 nm. By using Y-1 and Y-2 as photosensitizers for IOPF, E51 reach high epoxy conversions of 95% under light wavelength of 470-nm irradiation. IOPF and benzothiadiazole dyes present at the same time show good visible-light initiating activity. The high curing conversions are attributed to the photoelectron transfer reaction between diphenyliodonium hexafluorophosphate and benzothiadiazole dyes, based on our photochemical and electrochemical experiments. In addition, the terminated groups or of Y-1 (–F) and Y-2 (–OCH 3 ) have a great influence on the photopolymerization rate of the curing systems and thermal properties of E51 after cured. In addition, E51 was even polymerized about 70% in the presence of 510-nm light filter.