Effects of the number and position of methoxy substituents on triphenylamine-based chalcone visible-light-absorbing photoinitiators

Five visible-light-absorbing triphenylamine-based chalcone photoinitiators (CY1–CY5) that contain peripheral triphenylamines at both sides with various methoxy substituents of the triphenylamine moiety have been synthesized for application in free radical photopolymerization. They were confirmed through 1H nuclear magnetic resonance (NMR), 13C NMR, and Fourier-transform mass spectrometry results. All the compounds exhibited near-ultraviolet (UV) and visible-light absorption with a maximum absorption peak at approximately 426 nm. The photochemical reaction behavior of the compounds was investigated through photolysis, cyclic voltammetry, electron spin resonance, and theoretical calculations. Chalcone derivatives in combination with triethanolamine (TEOA) as a coinitiator were prepared and employed to initiate the free radical photopolymerization of trimethylolpropane triacrylate (TMPTA) by using a photo-DSC instrument. The CY1-based formulation exhibited the highest final conversion efficiency under UV lamp irradiation (43%), whereas the CY4-based formulation had the highest efficiency under 405 nm LED light irradiation (43%). In this study, the effects of the methoxy position and different-wavelength light sources were clearly investigated and discussed.