Radical Photopolymerization Using 1,4-Dihydropyrrolo[3,2-b]pyrrole Derivatives Prepared via One-Pot Synthesis

Radical photopolymerization has attracted significant attention for manufacturing products with complicated structures. Herein, the synthesized 1,4-bis(4-bromophenyl)-2,5-bis(4-nitrophenyl)-1,4-dihydropyrrole[3,2-b]pyrrole (PyBN) is found to show varying photoactivity upon irradiation at different wavelengths. PyBN affords two main absorption bands, and its maximum absorption peak is at 462 nm, attributing to its strong intramolecular charge transfer property based on the donor-acceptor structure. It efficiently photoinitiates the radical photopolymerization of different (meth)acrylate materials under 365 and 395 nm LED irradiation. The highest double bond conversion of 99.86% is achieved for these materials. Under 470 nm LED, PyBN does not show molecular structure change from photolysis results as a result of intramolecular charge transfer. Therefore, PyBN shows wavelength-selective photoactivity with potential application in dual-wavelength volumetric additive manufacturing. A unique solid product is successfully fabricated using a 365 nm LED with co-irradiation of a 470 nm LED. Additionally, PyBN incorporating camphorquinone (CQ) as a two-component visible light photoinitiator system is investigated under 470 nm LED irradiation. As PyBN has a charge transfer activity at 470 nm, the combination with CQ exhibits a good synergistic interaction. Besides nitro-based PyBN, a methyl-based PyBC was prepared as a reference compound.