2D-QSAR-DFT assisted design of unimolecular coumarin oxime ester photoinitiators with terminal fluorobenzene moieties for radical polymerization

Coumarin oxime esters (COXEs) have received extensive attention for their outstanding photoinitiation performance, but their rational and efficient design is challenged by the vast combinatorial space of possible electron donor/acceptor substituents on the coumarin core. In this work, a two-dimensional quantitative structure-activity relationship (2D-QSAR) analysis of reported COXE structures was performed to examine the relationship between structural descriptors and photo-reactivity. It was revealed that the acceptor and donor of hydrogen bond (HA, DH), total energy ( E ), as well as energy gap ( E g ) strongly influence the absorption wavelength ( λ max ). In particular, the phenyl ring with electron-withdrawing substituents enhances the charge asymmetry of the adjacent N–O bond and induces a red shift in the absorption wavelength. As a result, a novel COXE, namely C-5, was rationally designed and synthesized with a pentafluorophenyl substituent. The λ max of C-5 was predicted by DFT and confirmed by the UV-vis spectrum to be 424 nm in acetonitrile. Meanwhile, C-5 exhibits strong absorption ( ε ) of about 8.66 × 10 3  M −1  cm −1  at 405 nm and shows rapid photobleaching under 405 nm irradiation. In addition, the GelNB system photocured by the C-5 photoinitiator enabled a polymerization conversion of about 25.8%, with an elastic modulus of 2878 MPa. This modulus is significantly higher than that of the samples cured by the LAP and Irgacure 2959. These results demonstrate that the 2D-QSAR-DFT collaborative design can identify and optimize novel COXE photoinitiators, thereby advancing the highly efficient, rational preparation of visible-light-active photoinitiators for visible-light photopolymerization.