Triphenylamine based benzylidene ketones as visible-light-absorbing Type II photoinitiators for free radical photopolymerization

[Display omitted] •Double triphenylamine benzylidene ketones (C1F–C4F) bearing different cores were synthesized.•The effects of alkane or alicyclic ring cores on the various properties were investigated.•TMPTA monomer can be initiated for photopolymerization by C1F–C4F/TEOA photoinitiating packages under UV, LED@405 nm and LED@468 nm exposures. In this study, four Type II visible-light-absorbing triphenylamine benzylidene ketones (C1F–C4F) for radical photopolymerization were synthesized. The design strategy for ketone-cores involved the use of cyclobutanone for C1F, cyclopentanone for C2F, cyclohexanone for C3F, and acetone for C4F. The structures were confirmed by 1H NMR, 13C NMR, and mass spectrometry, respectively. The triphenylamine benzylidene ketones had good light harvesting ranging from 350 to 500 nm. In addition, the core effects with alkane or alicyclic rings on the photophysical, thermal, photochemical and electrochemical properties for these compounds were investigated systematically. Finally, the photopolymerization experiments demonstrated that trimethylolpropane triacrylate (TMPTA) monomer can be initiated for photopolymerization by triphenylamine benzylidene ketones (C1F–C4F)/triethanolamine (TEOA) photoinitiating systems under UV, LED@405 nm and LED@468 nm exposures. Particularly, C4F based formulation exhibits the best double bond conversion efficiency under UV and LED@468 nm exposure. On the other hand, C1F based formulation exhibits higher photoreactivity under LED@405 nm irradiation condition. This work thus demonstrates the introduction of different cores into the benzylidene, which can fine-tune the photopolymerization characteristics and let these novel photoinitiators promising candidates for industrial applications.