Highly efficient one-component benzylidene cyclopentanone initiators for visible light polymerization

Visible light polymerization is a development trend in the field of photocuring. However, most of the reported visible light photoinitiators (PIs) are two-component systems that display limited initiation efficiency due to diffusion restriction and back electron transfer effect. In this study, two one-component visible light PIs (BDNPG-1 and BDNPG-2) are synthesized through combining N-phenylglycine (NPG) moiety with cyclopentanone moiety together. Upon irradiation of blue or green light, they can undergo intermolecular electron transfer followed by proton transfer plus a decarboxylation reaction to produce carbon dioxide and aminoalkyl radicals. This decarboxylation reaction is irreversible so that the intermolecular back electron transfer can be effectively blocked, resulting in a significantly improved photoinitiation efficiency of BDNPG-1 and BDNPG-2 compared with their prototype PI (BDEA) containing no NPG group and the two-component system of BDEA+NPG. Furthermore, both of them have strong two-photon absorption capability and show excellent performance in two-photon polymerization.