Studies on an argon laser-induced photopolymerization employing both mono- and bischromophoric hemicyanine dye–borate complex as a photoinitiator

Dye photoinitiators consisting of either 1,3-bis-[4-(p-N,N-dialkylaminostyryl)pyridinyl]propane (C1B2–C8B2) or 1,3-bis-[4-(p-N,N-dialkylaminostyryl)-pyridinyl]xylene (A1B2–A8B2) dications, acting both as light absorbers and as electron acceptors and n-butyltriphenylborate anions being electron donors were tested in order to reveal the effect of a dye structure on the efficiency of multiacrylate photoinitiated polymerization. The kinetic studies clearly demonstrated that the bischromophoric stilbazolium borate photoredox pairs exhibit a significant increase in the efficiency of TMPTA free radical polymerization in comparison to the pairs containing structurally related, monochromophoric styrylpyridinium borates (SP1B2–SP8B2). The efficiency of tested systems depends on the ΔGel of electron transfer between borate anion and styrypyridinium cation. The latter value was experimentally determined for 24 photoredox pairs. The relationship between the rate of polymerization and the free energy of activation of electron transfer reaction shows the dependence predicted by the classical theory of electron transfer phenomena. This relation is independently observed for mono- and bischromophoric hemicyanine borate salts.