High Refractive Index Carbonized Polymer Dots: Multifunctional Nano‐Building Block for Optical Materials

High refractive index (RI) nanoparticles are crucial for the development of high-RI materials. However, traditional inorganic nanoparticles often require complex surface modifications to enhance their compatibility with polymer matrices, which leads to a reduction in RI. Additionally, the level of doping is still limited by certain limitations. Carbonized polymer dots (CPDs) are a new type of nanoparticles that exhibit polymer-like characteristics, which can be used as a nano-building block to construct macroscopic materials. Herein, sulfur-doped CPDs (Tp-CPDs) are successfully synthesized, which possess RI of 1.7606 at 589 nm. Tp-CPDs can be directly hybridized with a polymer matrix to fabricate nanocomposites, which exhibit continuously tunable RI ranging from 1.5180 to 1.7606 at a wavelength of 589 nm. Following a further crosslinking process, the film assembled from Tp-CPDs exhibits a higher RI (1.7808 @589 nm) and good stability. Furthermore, because of the abundant functional groups on the surface, Tp-CPDs can be readily surface-modified. The modified Tp-CPDs possess good processability and re-castability, which can be used in thermal nanoimprint lithography to precisely produce photonic crystal structures.