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 >350 nm, 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 380 nm. TX-A itself does not have phosphorescence emission; however, diTX-A displayed phosphorescence emission spectrum similar to thioxanthone. IR and 1H 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.