Multifunctional Photobleaching\nVisible Radical/Cationic\nPhotoinitiators Based on 5‑Membered Aromatic Heterocyclic-Bis-Chalcone-Oxime\nEsters

Three photobleachable photoinitiators (PIs) with bis-chalcone-based\noxime esters (PBAs) are designed and synthesized, including the electron\ndonor (D) of a 5-membered aromatic heterocyclic (furan, thiophene,\nand pyrrole), electron acceptors (A) of cyclopentanone carbonyl, and\noxime acrylate for visible photopolymerization. The mechanism for\nthe generation of oxygen alkyl radicals, 5-membered aromatic heterocyclic\nradicals, and vinyl radicals demonstrates that PBAs are characterized\nby type I and type II PIs. Real-time Fourier-transform infrared (FT-IR)\nspectroscopy indicates that PBAs, effective one-component PIs, are\nable to rapidly initiate the photopolymerization of the double-bonded\nmonomer when exposed to LED@385∼455 nm. In particular, PBA3\nwith pyrrole as D exhibits the highest double-bond conversion efficiency\nand photobleaching characteristics, and its acetonitrile solution\ncompletely fades within 8 min under LED@455 nm exposure. Moreover,\nthe colorless bulk acrylate materials with thicknesses of up to 40\nmm are produced through photopolymerization initiated by PBA3. Furthermore,\nPBA3/Iod as a two-component PI efficiently initiates hybrid photopolymerization\nof the double-bonded monomer and epoxy monomer to form an interpenetrating\npolymer network. Notably, PBA3 exhibits only a 1.9% migration ratio\nfrom polymerization films under illumination (60 min). Consequently,\nthe research results provide an innovative avenue for the structural\noptimization of photobleaching PIs and extend their applicability\nto the field of deep photocuring.