Photopolymerization under various monochromatic UV/visible LEDs and IR lamp: Diamino-anthraquinone derivatives as versatile multicolor photoinitiators

Diamino-anthraquinone derivatives [1,4-bis(isopropylamino)anthraquinone (SB36), 1-amino-4-anilinoanthraquinone (SB68), and 1,4-bis(p-tolylamino)anthraquinone (SG3)] exhibit absorption maxima in red light wavelength range and demonstrate broad ground state light absorption from ultraviolet to infrared light. When combined with coinitiators (e.g. iodonium salt), SB36-based photoinitiating systems exhibit the highest photo initiation efficiency among all the studied diamino-anthraquinone derivative-based combinations for both cationic and free radical photopolymerization upon exposure to a red LED bulb. And SB36-based systems even demonstrate higher photoinitiating ability for free radical photopolymerization than that of previously studied 1,4-bis(pentylamino)anthraquinone (i.e. oil blue N)-based systems. In contrast, SG3-based photoinitiating systems show the lowest photoinitiation efficiency especially for free radical photopolymerization. Interestingly, the SB36/iodonium salt/N-vinylcarbazole system is a capable multicolor photoinitiating system able to initiate both cationic and free radical photopolymerization under the irradiation of UV to red LED bulbs and IR lamp. The photochemical mechanism associated with the production of cations and radicals from the diamino-anthraquinone derivative-based photoinitiating systems are investigated using steady state photolysis, fluorescence, laser flash photolysis, and electron spin resonance spin-trapping techniques.