Fluorene-Derived High-Refractive-Index Polymers with Superior Optical and Thermal Properties for Advanced Optical Components

The advantages of polymeric optical materials over glass include low density, cost-effectiveness, and high impact resistance, making them well-suited for photonic and optoelectronic applications. However, the low refractive indices and thermal stability of conventional optical polymers constrain their use in high-performance systems. To overcome these limitations, we designed and synthesized three fluorene-based monomers (Fluorene-Xanthene (FX), Fluorene-Thioxanthene (FTX), and Fluorene-Thioxanthene-Dioxide (FTXDO)) via the heteroatom-assisted ring closure of diaryl groups at the 9,9′-positions of the fluorene cardo core, thereby enhancing electron density and polarizability. The monomers were polymerized into polycarbonates, polyurethanes, polyacrylates, and epoxy resins, which exhibited excellent optical transparency (up to 99.4% transmittance at 550 nm), high refractive indices (up to 1.730 at 589 nm), and enhanced thermal properties (decomposition temperature up to 373 °C, glass transition temperature up to 195 °C). Thus, these high-refractive-index polymers have been identified as promising candidates for cutting-edge optical systems due to their broad utility and superior performance characteristics.