Chemistry and Technology of Upconversion Material-Assisted Near-Infrared Photopolymerization: An Emerging Strategy for Photopolymerization

Upconversion materials (UCm)-assisted near-infrared (NIR) photopolymerization (UCAP) has gained increasing attention for its ability to convert NIR light into UV-vis light to initiate polymerization. In this perspective, we first present the mechanisms of stepwise multiphoton absorption in UCm and the composition of UCAP, emphasizing the design of efficient photoinitiation systems. The current state of UCAP research is reviewed across different polymerization mechanisms, including free-radical, cationic, and reversible-deactivation free-radical polymerization. In addition, key factors affecting UCAP efficiency─such as UC material design, photoinitiator properties, laser power, and formulation parameters─are systematically analyzed. UCAP shows broad potential in advanced coatings, multiscale additive manufacturing, and biomedical engineering. Despite being in its early stages and facing many challenges, UCAP provides a transformative pathway for designing and fabricating next-generation functional materials.