12H-Quinoxalino[2,3-b][1,4]benzothiazine derivatives as novel visible photosensitizers in cationic photopolymerization

Photoredox pairs consisting of dyes based on a 12H-quinoxalino[2,3-b][1,4]benzothiazine skeleton and iodonium salt are found to be effective initiation systems for cationic polymerization of epoxide monomers and tetrahydrofuran using VIS light. The efficiency of these initiator systems is discussed on the basis of the free energy change for electron transfer from benzothiazine dyes to the iodonium compounds. Three products, phenyl derivatives of dye 1 were isolated after photolysis of 1/onium salt system. These compounds were characterising by chemical ionization mass spectra. The reactions created the phenylated analogues of dye 1 and protons were proposed.