New functionalized thioxanthone derivatives as type I photoinitiators for polymerization under UV-Vis LEDs

The development of effective Vis-sensitive photoinitiators for light-emitting diode (LED) polymerization is still an emerging challenge as LEDs are being developed into the predominant light sources. In this work, a series of new functionalized photoinitiators, containing thioxanthones and oxime-esters as functional groups, was designed and straightforwardly synthesized in two steps. The structures of the photoinitiators were studied using H-1 NMR, C-13 NMR, and high-resolution mass spectrometry. The conclusion of the photophysical properties indicated that the long wavelength absorptions from 360 nm to 405 nm made the investigated thioxanthone derivatives quite appealing as a valuable photoinitiator under UV-Vis LEDs. The structure-reactivity relationship was also studied in detail through real-time FTIR spectroscopy. A possible photolysis mechanism was expected based on further photolysis and online H-1 NMR activities. With a proper molecular design, the new functionalized photoinitiators were synthesised straightforwardly and they displayed more advanced initiation abilities than their parent thioxanthone.