Structure-property relations of chiral polyfluorene derivatives

There has been growing interest in studying chiral polymers both theoretically and experimentally due to their potential application in the field of negative refractive index metamaterials. Large optical activity of these polymers, combined with their excellent flexibility and processability holds a great promise for a wide range of technological applications. In order to prepare such materials, its desirable that the polymer backbone presents a helical assembly behavior, generally incorporating asymmetric chiral centers to the monomer units. The resulting materials are characterized by a chirality parameter, κ, and can be measured by the circular dichroism (CD) technique. In this way, the synthesis along with a systematic study of a series of chiral polyfluorene derivatives was made, aiming to identify the main properties controlling the chiroptical activity of polymer films. For each polymer, five empirical/theoretical properties were chosen, due to their effect on the chirality parameter: glass transition temperature, dissymmetry factor, molar mass, helix tightness and the inverse of interconversion energy. A radar graph was built, exhibiting the influence of these five parameters and their interplay. The polygonal area in the radar graph and κ presented a direct relationship. Such graph can provide prescreening of polymer properties, based on both experimental measurements and theoretical considerations and help to choose the right combination of parameters, leading to a material with the best properties.