Benzothiazine Dyes/2,4,6-Tris(trichloromethyl)-1,3,5-triazine as a New Visible Two-Component Photoinitiator System

Abstract

Novel photoinitiator systems working under visible radiation were studied. The photoredox pair constructed with dye derivatives of 12H-quinoxalino-[2,3-b][1,4]-benzothiazine (1–3) and 2,4,6-tris(trichloromethyl)-1,3,5-triazine (Tz) were found to be effective initiators for free radical polymerization of trimethylolpropane triacrylate (TMPTA) using VIS light. Photosensitization occurred through electron transfer, which was confirmed by the observation of a radical cation of the studied dyes. The 1•+ was also characterized in cryogenic matrices (mixture of CH2Cl2 and ionic liquid: 1-butyl-3-methylimidazolium hexafluorophosphate ( −)) and its reactivity was investigated by means of pulse radiolysis in solution at room temperature. In a halogenated solvent and in a mixture of CH2Cl2 and −, the radical cation 1•+ underwent deprotonation to form a neutral radical 1•, which was stable in the second time scale. During photolysis of the 1/Tz photoredox pair in 1-methyl-2-pyrrolidone and monomer, the formation of a neutral radical 1• was not observed.