Symmetrically-substituted Thiazolo[5,4-d]thiazole derivatives as both photoinitiators and dyes for 3D printing under violet LED

The outstanding photochemical properties of thiazolothiazole and its derivatives make them attractive as po-tential photoinitiators. Two homosubstituted thiazolo[5,4-d]thiazole derivatives, 2,5-di(furan-2-yl)thiazolo[5,4-d]thiazole and 2,5-di(thiophen-2-yl)thiazolo[5,4-d]thiazole, were investigated as photoinitiators for both the free radical and the cationic polymerization upon the light irradiation from LED@410 nm. In particular, steady-state photolysis, fluorescence quenching experiments, and electron paramagnetic resonance spin-trapping techniques were used to study their photochemical mechanisms in generating active species. When coupled with one or two additives, these thiazolothiazole-based photoinitiating systems showed effective photoinitiation abilities on both the free radical and the cationic photopolymerization. Specifically, 2,5-di(furan-2-yl)thiazolo [5,4-d]thiazole-and 2,5-di(thiophen-2-yl)thiazolo[5,4-d]thiazole-based photoinitiating systems were found to be of similar efficiency on the free radical photopolymerization of trimethylolpropane triacrylate and the dental resin (the blend of bisphenol A glycidyl methacrylate and triethylene glycol dimethacrylate) with minor shrinkage but presented different performance in cationic photopolymerization of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate. Moreover, the curing depth of the samples and 3D printing capability were also investigated to determine their potential applications.

Automated summary

This study investigated two homosubstituted thiazolo[5,4-d]thiazole derivatives as photoinitiators for both free radical and cationic polymerization, under LED@410 nm light irradiation. The results showed that these photoinitiating systems exhibited effective initiation abilities in both types of polymerization reactions, with variations in efficiency and performance depending on the polymer system.