Highly Efficient and Cytocompatible Panchromatic Photoinitiators for Photopolymerization and High-Resolution 3D...

This study comprehensively elucidated the wavelength-responsive range of phenothiazine photoinitiators (P1 and P2) and the mechanism of single electron transfer (SET) between them and iodonium salt (Iod). Theoretical calculations provided precise predictions regarding the thermodynamic feasibility, electrochemical driving force, and preferred SET pathway of this reaction. These conclusions were quantitatively confirmed through photophysical characterization, electrochemical analysis, and electron spin resonance spin-trapping investigations. Unlike many conventional photoinitiating systems that remained ineffective beyond the blue light spectrum, the P2 compound exhibited a broad initiation window spanning from near-ultraviolet to red light. Notably, during photopolymerization under red light irradiation, the P2/Iod system achieved a reaction rate approximately six times faster than that of the previously reported phenothiazine derivatives. Furthermore, the P1/Iod and P2/Iod systems maintained excellent photoinitiation performance under sunlight and smartphone flashlight irradiation. Importantly, the P1/Iod system enabled long-wavelength (460 nm) digital light processing (DLP) 3D printing with micrometer-scale surface features. In addition, P1 showed significantly lower cytotoxicity than the commercial photoinitiator diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO) at high concentrations. These findings offer a rational strategy for the design of low-toxicity and panchromatic photoinitiating systems for high-precision additive manufacturing.