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

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