Controlling Polymer Solubility: Polyfluorenes with Branched Semiperfluorinated Side Chains for Polymer Light-Emitting Diodes

A series of novel polyfluorenes, soluble exclusively in perfluorinated solvents, were prepared. The new materials were studied with regard to orthogonal processing of organic electronic materials. The desired solubility was achieved by introducing semifluorinated side chains to the fluorene monomers. Since the use of long perfluoroalkyl chains (RF) is restricted due to public health concerns, a synthetic route for polyfluorenes with short RF chains branched by aromatic units has been developed. The photophysical behavior of the resulting polymers was investigated in solution and thin films by UV/Vis absorption and photoluminescence spectroscopy. The photoluminescence quantum yields were found to be in the range of those of alkylated polyfluorenes. The electroluminescent properties were studied in single-layer polymer light-emitting diodes, with the new polymers as active materials, which exhibited similar characteristics to previously published single-layer devices with polyfluorenes containing long RF. The wetting properties of different polyfluorene films containing fluorinated, polar, polyethylene glycol, or nonpolar alkyl groups were investigated by contact angle measurements.