Robust High-Refractive-Index Polymer Films Enabled by a Bismuth-Dithiocarbamate Structure

High-refractive-index polymers are essential materials for advanced optical devices. However, simultaneously achieving a high refractive index, material stability, and polymer processability remains challenging, particularly in systems containing heavy elements. In this study, we developed a molecular design strategy based on Bi-S bonding and synthesized a radical-polymerizable bismuth-dithiocarbamate monomer. Bulk polymerization of this monomer afforded a self-supporting bismuth-containing polymer film. The resulting polymer exhibited a high refractive index (n_D = 1.75), attributed to the strong polarizability of both sulfur and bismuth, and demonstrated good thermal, photochemical, organic solvent, and water stability. Although the polymer film was orange, it combined a high refractive index with high material stability, making it suitable for wavelength-selective optical applications, such as near-infrared optics. Notably, this study represents the first evaluation of refractive-index properties in polymeric materials incorporating Bi-S bonds, providing new molecular design guidelines for high-refractive-index polymers.