Styrylquinolinium borates as donor–acceptor initiators for sensitized photopolymerization of TMPTA

Several photoredox pairs containing mono- and bicationic hemicyanine dyes have been evaluated as photoinitiators for free radical polymerization induced with an argon-ion laser irradiation. The tested photoredox couples are the pairs composed of the hemicyanine dye cations acting as electron acceptors and n-butyltriphenyl borate anions being the electron donors. The photoinitiating abilities of the series of monochromophoric stilbazolium borates, 4-(p-N,N-dialkylaminostyryl)quinolinium n-butyltriphenylborate, were compared to the photochemistry of structurally related, bicationic styrylquinolinium borates. The obtained results clearly documented that the dicationic photoinitiators exhibit a marked increase in the photoinitiation ability compared to the initiators consisting of a single charged hemicyanine dye. Our studies revealed also that the rate of photopolymerization depends on ΔGel of electron transfer between borate anion and styrylquinolinium cation. The relationship between the rate of polymerization and the free energy of activation shows the dependence predicted by the classical theory of electron transfer.