Monomeric asymmetric two- and three-cationic monomethine cyanine dyes as novel photoinitiators for free-radical polymerization

Several two- and three-cationic monomethine cyanine dyes, possessing a benzothiazolium moiety were synthesized and evaluated as initiators of the free radical polymerization of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol triacrylate under visible light. Dyes bearing 1-methylpyrrolidinium, 4-methylmorpholinium, pyridinium and 3-(N,N-dimethylamino)propan-1-ol substituents were useful initiators. All derivatives absorbed in the region 510–570 nm and displayed molar absorption coefficients of 40 000–60 000 dm 3 mol −1 cm −1. A kinetic study of photoinitiated polymerization performed with the use of the electron donor n-butyltriphenylborate salt showed that the dyes were efficient two-component photoinitiators.