Synthesis and optical studies of conjugated polyfluorenyl cations

Polyfluorene based precursor polymers were synthesized either by Yamamoto type or Suzuki polycondensation. These polymers were then converted to the corresponding conjugated polycations by treatment with trifluoroacetic acid. The formation of the conjugated polycations were followed by UV–vis and characterized by 1H NMR. The absorption maxima of the polycations fall in the range of 580–690 nm. The formation of the polycations is evidenced by a red shift in absorption maxima compared to the parent polymers due to the generation of stable cations with more extended conjugation and planarity. The cationic polymers show low solubility in common organic solvents, however the solubility of the cationic salt can be greatly enhanced by controlling the cation density along the polymer chain by copolymerization.