A Trifluoromethyl-Containing Pyrrolo3,2-bpyrrole Photoinitiator with Long Wavelength in Radical Photopolymerization under LED Irradiation

Pyrrolo3,2-bpyrrole is a good building block for radical photoinitiators. In this study, free-radical photoinitiator 1,4-bis(4-bromophenyl)-2,5-bis(4-(trifluoromethyl)phenyl)-1,4-dihydropyrrolo3,2-bpyrrole (PyBF), containing a symmetric trifluoromethyl (-CF₃) end group, is synthesized via a one-step aldehyde–ketone condensation reaction for light-emitting diode (LED) photopolymerization. The -CF₃ groups are incorporated into the 2,5-phenyl on the pyrrolo3,2-bpyrrole core. PyBF rapidly initiates the photopolymerization of acrylate prepolymers and monomers under LED illumination at 365 and 405 nm. A possible photolysis mechanism is provided. In the presence of amines, PyBF increases the gel fraction rate of polyethylene glycol diacrylate (PEGDA) from 63.4% to 80.0%, indicating good potential as a two-component photoinitiator. PyBF exhibits a thermal decomposition temperature in an excess of 300 °C, comparable to that of a commercial photoinitiator (diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, TPO), indicating its thermal stability. PyBF shows low migration in light-curing materials. Scanning electron microscopy images indicate that the materials of the PyBF/TPO/PEGDA mixture cured using the PyBF/TPO two-component photoinitiator system exhibit a smooth surface, in contrast to those cured with PyBF/PEGDA and TPO/PEGDA systems. The cured materials also display low curing shrinkage. Therefore, the pyrrolo3,2-bpyrrole radical photoinitiator exhibits high photoactivity in visible-light photopolymerization reactions.