Heterostructured Photoinitiator Comprising Upconversion Particles and Metal-Organic Frameworks for Enhanced Near-Infrared Photopolymerization: Implications for 3D Printing

Upconversion particle (UCP)-assisted near-infrared photopolymerization (UCAP) is an important photopolymerization technology that uses UCPs to convert near-infrared light into ultraviolet light to achieve the curing of photosensitive resins. However, the inherent low upconversion luminescence efficiency of UCPs, coupled with the significant photon loss during the propagation process within the material, significantly hampers the energy transfer efficiency between upconverted materials and photoinitiators, thereby restricting the broader applicability of this technique. In this work, a heterostructured photoinitiator comprising UCPs and metal-organic frameworks (UCPs@MOFs) was prepared via electrostatic interaction. The photoinitiator was loaded within the MOFs to achieve the integration of UCPs, MOFs, and photoinitiators, all with the goal of enhancing the curing efficiency of UCAP. The results revealed that the construction of the heterostructured photoinitiator significantly reduces the distance between UCPs and photoinitiators, thereby optimizing the utilization of upconverted fluorescence. This not only leads to accelerated polymerization rates but also achieves superior functional group conversion efficiencies. The cured materials obtained by this strategy have excellent mechanical properties, and the tensile strength increases from 25.8 to 47.3 MPa. By implementing this strategy in the realm of three-dimensional (3D) printing with near-infrared light-cured ink, the resulting printed materials exhibit superior conformability along with enhanced precision, demonstrating their potential for application in 3D additive manufacturing.