Cyanine/iodonium salt as a broad-absorbing photoinitiating system for radical photopolymerization under near-UV, visible and NIR light

Photoinitiators (PIs) and photoinitiating systems (PISs) which possess great broad-absorbing capability are extremely convenient in practical applications because they have very low selectivity for irradiation sources. Cyanines have excellent properties of light absorption in the near-infrared (NIR) region, in addition, certain absorptions of cyanines in the 400 nm-700 nm region are also worthy of attention. We investigated the photoinitiating capacities of four cyanines with iodonium salt (Iod) systems respectively to initiate radical photopolymerization at exposure to 808 nm NIR laser, 630 nm light-emitting diodes (LED), 450 nm LED and 400 nm ultraviolet (UV)-LED. Among the four investigated photoinitiating systems, the S2265 (one of the investigated cyanines)/Iod system exhibited remarkable stability of photoinitiating capacity no matter what irradiation of light source. The S2024, S2025, and S2025B (the other three investigated cyanines)/Iod systems are functional at exposure to 808 nm laser, 450 nm LED and 400 nm UV-LED. The photoinitiating capacities and photoinitiating mechanisms of the cyanine/Iod systems were explored by methods such as fluorescence, photolysis, thermal imaging, and so on. This work elucidates the photochemical behaviors of cyanines with exposure to near-UV and visible light, simultaneously, the research results reported in this work are valuable for exploring broad-absorbing photoinitiating systems used in photopolymerization under irradiation from multifarious light sources. Cyanine/iodonium salt as a broad-absorbing photoinitiating system for radical photopolymerization under exposure to near-UV, visible and NIR light.