Novel di-2-thienyl ketone derivatives photoinitiators enable fast visible light polymerization and 3D printing

A series of Type II photoinitiators (PIs) bis(5-(4-(diethylamino)phenyl)thiophen-2-yl)methanone (EATM), bis(5-(9-ethyl-9H-carbazol-3-yl)thiophen-2-yl)methanone (ECTM) and bis(5-(4-(diphenylamino)phenyl)thiophen-2-yl)methanone (PATM) based on di-2-thienyl ketone were synthesized for the visible light photoploymerization. The maximum absorption wavelengths of EATM, ECTM and PATM in DMSO were 437 nm, 455 nm and 477 nm, respectively. The fast photopolymerization of polyethylene glycol diacrylate (PEGDA) could be initiated in a three-component system consisting of photoinitiator, diphenyliodonium hexafluorophosphate (Iod) and triethanolamine (TEOA) under visible light. The conversion rate of CC bond under different light sources (405 nm, 440 nm and 480 nm) were measured by real-time Fourier transformed infrared spectroscopy (RT-FTIR). The CC bond conversion rate of PATM reached >93 % within 5 s, and the final conversion was up to 98 %, and the polymerization was completed in 10 s. The mechanism of light initiation was analyzed by density functional theory (DFT), steady-state photolysis and electron spin resonance spin trapping (ESR) experiments. Photobleaching, deep photocuring, migration ratio and cytotoxicity were evaluated. Three PIs were used to realize rapid 3D printing in an LCD 3D printer (405 nm). The printing rate was as high as 90 mm h⁻¹ with exposure time 2 s/layer. This study provides ideas for the development of PIs for fast photopolymerization and 3D printing under visible light.