Hydrogen self-supplying initiators excited by visible light for the fabrication of transparent films

Unimolecular Type II radical photoinitiators (PIs) have received significant attention in photocuring owing to the fact that they improve the sustainability of the overall process compared with traditional Type II radical photoinitiators. However, the photopolymerization efficiency of unimolecular Type II radical photoinitiators is hindered by their short excitation wavelengths, poor photon capture abilities, and inefficient photobleaching performance. Herein, we report a coumarin-based self-sufficient initiator (C-NA), which is designed by integrating “hydrogen donor” and “hydrogen acceptor” into the coumarin framework and used for single-component visible light curing. C-NA exhibits a visible light absorbance and high molar extinction coefficient and is completely photobleached under the irradiation of 405 nm light-emitting diodes (LEDs). The formation of free radicals arises from the transfer of hydrogen from the diethylamino group to the coumarin framework, together with a highly efficient photodegradation process of C-NA. Finally, C-NA was successfully applied to prepare a transparent film material. Therefore, C-NA offers new insights into the design of promising unimolecular Type II radical photoinitiators for photocuring.