Design of Oxime Ester Photoinitiators Based on Methoxy-Substituted\nCoumarin Chromophores for LED Photopolymerization and 3D Printing

In\nthis study, a series of photoinitiators (PIs) were designed\nand synthesized based on methoxy substitution at the 6/7/8-positions\nof coumarin chromophores, including coumarin ketone (CKs) and coumarin\noxime esters (COXEs). The aim was to investigate the impact of the\nsubstituent position on the photosensation and photoinitiation properties\nof the PIs crucial for LED photopolymerization. It was observed that\nthe introduction of methoxy at the 6-position in both Norrish type\nI and type II PIs resulted in a relatively great absorption redshift\nand photoinitiation efficiency in a coumarin-based PI. The absorption\nof PIs was found to increase with the extension of irradiation time\nat 385–450 nm, a characteristic that can be harnessed in UV-curing\n3D printing applications to minimize extra radiation penetration.\nNotably, as a co-initiator, 6-COXE exhibited remarkable enhancement\nin vertical texture resolution and whiteness of the 3D printed parts.\nThese outstanding performances of 6-substituted coumarin-chromophore\nPIs indicate their potential for application in advancing photopolymerization\ntechnology, offering an approach to the design of high-performance\nPIs.