Bisbenzothieno[b]-fused BODIPYs in panchromatic photoinitiating for the free radical and cationic photopolymerization and application in 3D printing

Abstract: Polymerization reactions induced by lights occupy an increasing share in the area of polymer synthesis; however, the effective photopolymerization under visible light emitting diodes (LEDs) rather than UV still remains limited and deserves intensive research and development. In this contribution, a family of bisbenzothieno[b]-fused boron dipyrromethene (BODIPY) derivatives never tested for photopolymerization before were designed to contain seven fused aromatic rings with a broad absorption property and introduced with amine and iodonium salt to form three-component photoinitiating systems (PISs) for the first time. Remarkably, under the irradiation of visible lights, e.g. LED@405 nm and LED@660 nm, these PISs could initiate the free radical polymerization of acrylate monomers and cationic polymerization of epoxy monomers at room temperature with differed photopolymerization kinetics. This excellent initiation ability at both ends of the visible spectrum (i.e. with the highest and lowest photon energy) indicated a remarkable panchromatic initiation ability. The exceptional photochemical reactivity of these BODIPY dyes and the underlying photoinitiating mechanisms of the PISs were thoroughly investigated through steady-state photolysis, fluorescence quenching experiments, and theoretical calculations. Finally, three-dimensional patterns with excellent spatial resolution were successfully printed using the BODIPY dye with the highest photoinitiation efficiency via direct laser writing, highlighting its significant potential for 3D printing applications.