Push-pull benzophenone derivative-based visible photoinitiating systems: synthesis, characterization, properties, and application for free radical photopolymerization under LEDs.

This study presents four (4-benzylamino-3-nitrophenyl) (phenyl)methanone derivatives (BP-NBR). They exhibit broad absorption peaks in the wavelength region of 350-500 nm, exhibiting a fairly good overlap with the emission spectra of light-emitting diodes (LEDs). In the presence diaryliodonium (Iod) or ethyl 4-(dimethylamino)benzoate (EDB), BP-NBR show high efficiency, although they show low activity as one-component system upon LED exposure. The proposed mechanism is as follows: the benzophenone segment is inactive due to its non-coplanar benzene groups. Instead, the 2-benzylamino-nitrophenyl segment serves as the photosensitizer. Moreover, the para-substituent of the benzylamino group has an effect on its initiation efficiency. The photoinitiation rate offered by BP-NBR/EDB is faster than that offered by ‌the commercial photoinitiator 4-aminobenzophenone‌ (BPNMe2)/EDB system upon exposure to 450 nm LED light. Thus, BP-NBR exhibit application potential in long wavelength LED photopolymerization.