Chalcone-derived oxime esters with efficient photoinitiation properties under LED irradiation

As one of the most essential components in photocuring system, photoinitiators (PIs) exert a crucial influence on the properties of the cured product. However, commercially available PIs encounter challenges in simultaneously achieving efficient photoinitiation performance and excellent light absorption properties, significantly limiting their applications in various fields. Here, two bis-chalcones and four corresponding oxime esters (OXEs) were designed and synthesized as highly efficient PIs. Featuring a structure comprising bis-chalcone and two diphenyl sulfides, the conjugated systems in these compounds enhance their light-absorption properties in near-ultraviolet and visible region, effectively. Both the frontier molecular orbital simulations and excited state calculations suggest the contribution of sulfur atoms to electron delocalization and the formation of conjugated structure. Due to the high reactivity of the NO bond in OXE moiety, the four OXEs exhibit exceptional free radical photoinitiating ability in commercial acrylic monomers/oligomers with LED@365 nm as light source. Notably, one of them demonstrates superior performance in the photoinitiation of multifunctional crosslinker, achieving more than 70 % conversion within 3 s, coupled with outstanding absorption at 365 nm. These chalcone-based OXEs are considered to exert significant potential in the realm of free radical photocuring.