Hydrogen Bonds and Enhanced Aggregation Emission of Organic and Polymeric Fluorophores with Alternative Fluorene and Naphthol Units

In this study, fluorescent organic compound FN and polymer PFN with alternative fluorene and naphthol units were prepared to assess the influence of the hydrogen bonds (H-bonds) on the emission behavior. Both FN and PFN exhibit the enhanced aggregation emission behavior with enhanced emissions on solution mixtures of higher degree of aggregation. For solid FN and PFN films, the fractions of the H-bonded hydroxyl groups decrease upon being heated to high temperature, which results in aggregate dissociation and reductions in the aggregation emissions. Meanwhile, procedures leading to the increase of the H-bonds (such as shearing or enhanced aggregation by addition of nonsolvent in the solution preparative step) resulted in solid films with higher emission intensity. Variations on the H-bonds can be detected by infrared spectroscopy and are in line with the emission behavior.