Visible-Light-Responsive Water-Soluble Macromolecular Photoinitiators Based on an Indole–Chalcone Core for Aqueous 3D Printing

The development of high-performance photoinitiators (PIs) capable of operating under visible light, exhibiting high water solubility and possessing macromolecular characteristics, remains a significant challenge in advancing sustainable photopolymerization technologies. Although recent research strategies focusing on visible-light activation, water solubility, or macromolecular design have achieved notable progress, they have only partially overcome the limitations associated with these properties. A visible-light-responsive, water-soluble, macromolecular photoinitiator (DIDP-mPEG) was developed based on an indole–chalcone core. DIDP-mPEG was synthesized via UV-induced grafting of poly(ethylene glycol) monomethyl ether (mPEG) chains onto a dual-photoresponsive precursor. The resulting initiator exhibited excellent water solubility (up to 5 wt %) and a high molar extinction coefficient at 465 nm. It efficiently initiated the aqueous polymerization of acrylamide, achieving >80% conversion within 360 s, and enabled the digital light processing 3D printing of hydrogels. The initiation mechanism, investigated through nuclear magnetic resonance (NMR) spectroscopy, photolysis, theoretical calculations, and kinetics, is proposed to involve hydrogen abstraction from the PEG chains by the excited chalcone carbonyl. Compared to benchmark macromolecular PIs, such as PEG-BAPO, DIDP-mPEG exhibits an enhanced molar extinction coefficient and superior initiating efficiency, representing a significant advancement toward the design of green, efficient photoinitiating systems for advanced aqueous photopolymerization applications.