For various optical applications, the fabrication of nanocomposites of co-polyarylidene (cyclohexanone/4-tertiary butyl cyclohexanone) CoP6 with various-sized cadmium sulfide CdS nanoparticles via in situ polymerization has been investigated (CoP6-CdS NCs). Several techniques like FT-IR, XRD, XPS, SEM, TGA, TEM, UV–vis, and fluorescence emission have been used to investigate, characterize, and study nanocomposites' structural and optical characteristics. The optical band gap of NCs was found to have a slight redshift, from 2.81 to 2.71 eV, with no alteration to the absorption peak. The crystallinity and phase formation were studied by XRD, which showed that the produced NCs with larger (CdS) particles retain some crystalline structure. The NCs generated were characterized by SEM and TEM, revealing their aggregation inside the polymer matrix. The thermal stability of the produced nanocomposites …