Ultrafast Sunlight-Induced Polymerization: Unveiling 2-Phenylnaphtho[2,3-d]Thiazole-4,9-dione as a Unique Scaffold for High-Speed and Precision 3D Printing.

A series of 15 dyes based on the 2-phenylnaphtho[2,3-d]thiazole-4,9-dione scaffold and 1 compound based on the 2,3-diphenyl-1,2,3,4-tetrahydrobenzo[g]quinoxaline-5,10-dione scaffold are studied as photoinitiators. These compounds are used in two- and three-component high-performance photoinitiating systems for the free radical polymerization of trimethylolpropane triacrylate (TMPTA) and polyethylene glycol diacrylate (PEGDA) under sunlight. Remarkably, the conversion of TMPTA can reach ≈60% within 20 s, while PEGDA attains a 96% conversion within 90 s. To delve into the intricate chemical mechanisms governing the polymerization, an array of analytical techniques is employed. Specifically, UV-vis absorption and fluorescence spectroscopy, steady-state photolysis, stability experiments, fluorescence quenching experiments, cyclic voltammetry, and electron spin resonance spin trapping (ESR-ST) experiments, collectively contribute to a comprehensive understanding of the photochemical mechanisms. Photoinitiation capacities of these systems are determined using real-time Fourier transformed infrared spectroscopy (RT-FTIR). Of particular interest is the revelation that, owing to the superior initiation ability of these dyes, high-resolution 3D patterns can be manufactured by direct laser write (DLW) technology and 3D printing. This underscores the efficient initiation of free radical polymerization processes by the newly developed dyes under both artificial and natural light sources, presenting an avenue for energy-saving, and environmentally friendly polymerization conditions.