Synthesis and characterization of diazafluorene-based oligofluorenes and polyfluorene

Diazafluorene (DAF) has a similar configuration to a fluorene unit except that two carbon atoms are replaced with nitrogen atoms, offering an ideal model of supramolecular conjugated polymers to investigate the structure-property relationship. Herein, a series of DAF-based oligofluorenes and polyfluorenes, including NFF, NF2F, F2NF, PFO-NO, PFO-N5, PFO-N15 and PFO-N50, have been synthesized by Suzuki and/or Yamamoto polymerization. All dioctyldiazafluorene-based copolymers show improved solubility, high quantum efficiency and good thermal stability. The 4,5-diazafluorenone (DAFone)-based oligomers exhibit solvent-dependent fluorescence and DAF-based copolymers show an optical response with a large red-shift (ca. 40-60 nm) of the absorption peak when they were protonated with trifluoroacetic acid. Their photoluminescent properties have also been obviously tuned by coordinating different metal ions to the polymers. DAF-based conjugated polymers are potential supramolecular polymer semiconductors for thin film electronics.