Synthesis and studies of novel homodimeric styrylbenzimidazolium dyes applied as photoinitiators for the radical polymerization of acrylic monomers

Abstract

A series of homodimeric styrylbenzimidazolium dyes were synthesized and applied as visible light initiators for the polymerization of acrylic monomer. In the photoinitiating system, hemicyanine dye cation acts as an electron acceptor whereas borate anion is an electron donor. The photochemistry of the series of bichromophoric hemicyanine borates: 1,3-bis{2-(4-(N-alkylamino)styryl)-1-methylbenzimida- zolium}propane, 1 ,5-bis{2-(4-( N-alkylamino)styryl)-1-methylbenzimidazolium}pentane, 1,10-bis{2-(4-(N-alkylamino)styryl)-1-methylbenzimidazolium}decane, was compared to the photoche- mistry of structurally related monochromophoric hemicyanine borates. The photoinitiating efficiency of the donor-acceptor pairs is discussed based on the free energy change for the photoinduced electron tran- sfer from borate anion to dye cation.