Trifluoromethyl-substituted pyrrolo[3,2-b]pyrrole derivatives for visible light photopolymerization

Three pyrrolo[3, 2-b]pyrrole compounds (Py–CF₃–H, Py–CF₃–CH₃ and Py–CF₃–OCH₃) were prepared as radical photoinitiators for visible light radical photopolymerization. Radical photopolymerization using the Py–CF₃–H initiator-induced TMPTA system achieved a peak conversion rate of 72% for C=C double bonds. The effect of changes in the electronic structure on the photoinitiation ability of the three photoinitiators was studied using spectroscopic measurements and theoretical calculations. The generated free radicals were detected using electron paramagnetic resonance (EPR). The synthesized photoinitiators matched the 405 nm LED. Under steady photolysis at 405 nm, the maximum absorption peaks decreased rapidly after exposure to light, and a new blue-shifted peak appeared. The end groups on the phenyl at 1,4 positions of the pyrrolo[3,2-b]pyrrole core considerably influenced the charge surrounding the central core, according to the electrostatic potential (ESP) results. The –H on 1,4-phenyl provides a less negative charge on the fused pyrrole core compared to the –CH₃ and –OCH₃. Thus, this work provides an experimental foundation for investigating pyrrole-based photoinitiators in polymer curing.