Naphthalimide Derivative-based Photoinitiating Systems for Multi-Wavelength Visible Light Photopolymerization and 3D Printing

Abstract

While naphthalimide derivatives have been widely explored in the design of photoinitiators, achieving robust photopolymerization performance across multiple visible wavelengths, particularly in longer-wavelength 3D printing, remains a significant challenge. This work presents two naphthalimide derivatives, denoted as NDI 1 and NDI 2, featuring a polymerizable methacryloyl group and a terminal hydroxyl moiety, respectively. Both dyes demonstrate the capability to initiate the photopolymerization of acrylate monomers either independently as one-component photoinitiators or in combination with bis(4-tertbutylphenyl)iodonium hexafluorophosphate (iodonium salt, Iod) upon irradiation with LED@405, 455, and 470 nm. With poly(ethylene glycol) diacrylate 700 (PEGDA 700) as the monomer, both two-component photoinitiating systems (PISs) achieve remarkable final double bond conversions exceeding 92%. Notably, NDI 2 exhibits superior performance, distinguished by its outstanding solubility and excellent storage stability, a key advancement for practical applications that maintains high activity after 30 days of storage. Finally, the practical utility of the NDI 2/Iod is validated through the successful fabrication of complex architectures using digital light processing (DLP) (at 405 nm and 460 nm) as well as single-photon direct laser writing (DLW) (with 405 nm and 455 nm lasers). These results establish NDI 2 as a robust and versatile photoinitiator for next-generation additive manufacturing.