Effect of Decarboxylation on the Photoinitiation Behavior of Nitrocarbazole-Based Oxime Esters br

A series of 50 oxime esters bearing various substituents were designed and synthesized as photoinitiators (48 of them were never synthesizedbefore and onlyB1andB10were reported). Good light absorption properties inthe visible range were observed for these oxime esters. Some structures exhibitedbetter photoinitiation abilities than diphenyl(2,4,6-trimethylbenzoyl)phosphineoxide (TPO) upon exposure to a LED@405 nm. Interestingly, PIs with methylsubstituent on the oxime ester group have better photoinitiation performance thanthe others. Substituent effects were investigated through molecular orbitalscalculations, the detection of CO2, and the investigation of the generated free radicals. The results demonstrate that the substituents on the oxime ester groupexert major effects on the photoinitiation ability via the decarboxylation reaction. In addition, a chemical mechanism was proposed.3D printed objects were successfully obtained by using the most reactive oxime ester as photo initiator, and their thermal initiation behaviors of several oxime esters were also studied (dual thermal/photochemical initiator behavior)