Novel nitro‐quinoline photoinitiators for composites: exploring the effects of hydroxyl and methacrylate substituents on the photopolymerization of dimethacrylate matrices

Photopolymerization has recently consolidated itself as a highly efficient and essential technology for developing advanced polymer networks, particularly biomaterials like dental composites. However, the performance and biocompatibility of light‐cured resins are often limited by incomplete monomer conversion and the potential toxicity associated with conventional photoinitiator (PI) systems typically based on camphorquinone (CQ). To overcome these challenges, this study presents the synthesis and structure–property evaluation of six quinoline‐based compounds as novel type II PIs, exploring the effects of positional isomerism and functional substituents on the polymerization process. Four of these experimental PIs are reported for the first time in this application and were tested in dimethacrylate matrices (urethane dimethacrylate and a bisphenol A‐glycidyl methacrylate/triethylene glycol dimethacrylate blend) using either ethyl‐4‐dimethylaminobenzoate (EDB) or glycerol (GLY) as coinitiators under UV and blue light irradiation, yielding intrinsically fluorescent polymers. GLY was investigated as a promising, eco‐friendly alternative to traditional tertiary amines. In general, the quinoline derivatives promoted rapid curing, with some systems achieving 50% conversion in 10 s and exceeding 75% after 300 s; when EDB was used as a coinitiator, these systems consistently outperformed CQ. Notably, systems utilizing GLY as an amine‐free co‐initiator yielded degree of conversion values above 57%, confirming its viability as a sustainable alternative for the development of new photoinitiation systems. Furthermore, the best‐performing PI systems were compared to the CQ‐based control regarding flexural strength, both in the presence and absence of inorganic fillers. The experimental composites demonstrated robust mechanical performance, achieving values equivalent to or superior to the control, with some formulations reaching over 138 MPa at 50 wt% inorganic filler loading. Overall, these findings establish a proof‐of‐concept for quinoline‐based PIs in composite dental resin formulations. Further studies addressing biological performance, particularly cytotoxicity and genotoxicity, are required before clinical translation.