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

Polymerization reactions induced by light are gaining increasing importance in the field of polymer synthesis; however, effective photopolymerization under visible light emitting diodes (LEDs), as opposed to UV light, remains limited and warrants further research and development. In this work, a family of bisbenzothieno[b]-fused boron dipyrromethene (BODIPY) derivatives, which have not been previously tested for photopolymerization, were designed. They contain seven fused aromatic rings with broad absorption properties and were introduced with amine and iodonium salt to form three-component photoinitiating systems (PISs) for the first time. Remarkably, under visible light irradiation, e.g. LED@405 nm and LED@660 nm, these PISs were able to initiate the free radical polymerization of acrylate monomers and cationic polymerization of epoxy monomers at room temperature, displaying different photopolymerization kinetics. This excellent initiation ability at both ends of the visible spectrum (i.e. the highest and lowest photon energy) indicated a remarkable panchromatic initiation ability. The exceptional photochemical reactivity of these BODIPY dyes and the underlying photoinitiation 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.