The synthesis of novel, visible-wavelength, oxidizable polymerization sensitizers based on the 8-halogeno-5,12-dihydroquinoxalino[2,3-b]quinoxaline skeleton

Novel dyes, based on the 8-halogeno-5,12-dihydroquinoxalino[2,3-b]quinoxaline skeleton, were synthesized and characterized using 1H NMR spectroscopy and chemical ionization mass spectroscopy. Their electrochemical and spectral properties, such as absorption and emission spectra, quantum yield of fluorescence and quantum yield of singlet oxygen generation, were also measured. These dyes were used as oxidizable sensitizers for diphenyliodonium and N-alkoxypyridinium salts. Photoredox pairs, consisting of dyes and pyridinium or iodonium salts, were found to be effective visible-wavelength initiators of free radical or cationic polymerization, respectively. The ability of each dye to act as a photoinitiator strongly depended upon its chemical structure. The heavy atoms present in the chemical structure could lead to excited triplet states within the dye, thereby facilitating electron transfer from these states.