Photodimerization of thioxanthone-anthracene: formation of monochromophoric Type II initiator

Abstract

Thioxanthone-anthracene (TX-A) was previously synthesized and used as an initiator for the polymerization of acrylates and methacrylates in air atmosphere. Photodimerization of TX-A was carried out in benzene under light irradiation of >350nm, and dimer (diTX-A) formation was followed by UV-vis, fluorescence and phosphorescence spectroscopy. The conjugation of anthracene was destroyed after dimerization, and the thioxanthone group was left behind. Therefore, the typical thioxanthone absorption spectrum was seen at 380nm. TX-A itself does not have phosphorescence emission; however, diTX-A displayed phosphorescence emission spectrum similar to thioxanthone. IR and H-1 NMR spectrophotometric techniques also helped to determine the structure of diTX-A. Furthermore, photopolymerization of methyl methacrylate (MMA) in the presence of dimer (diTX-A) was another proof of the photodimerization of TX-A. diTX-A initiated polymerization of MMA as good as thioxanthone in the nitrogen atmosphere and displayed typical Type II initiator behaviour.