Synthesis and Properties of High‐Refractive‐Index Iodine‐Containing Fluorene‐Based Polyesters

Polymers incorporating fluorene units have attracted considerable attention for advanced optical applications such as displays, lenses, and optical waveguides because of their high refractive index, good solubility, and excellent film‐forming ability. Here, motivated by reports that iodine‐containing polymers exhibit remarkably high refractive index values due to the large molar refraction of iodine atoms, we synthesize a fluorene‐based iodine‐containing monomer and examine its polycondensation with various dicarboxylic acid chlorides. The resulting iodine‐containing polyesters exhibit high thermal stability and good solubility in common organic solvents and afford uniform thin films by spin coating on a silicon wafer. The densities of the iodine‐containing polyesters are higher than that of non‐iodine‐containing polyester, and the refractive index values increase with increasing iodine content, reaching as high as approximately 1.672 at λ = 636 nm. These results indicate that fluorene‐based iodine‐containing polyesters are promising candidates for novel high‐refractive‐index optical materials.