Polyfluorenes with phosphonate groups in the side chains as chemosensors and electroluminescent materials

Polyfluorenes (P1 and P2) with phosphonate groups in the side chains were designed and synthesized. Their absorption and photoluminescence spectra in solutions are solvent dependent and exhibit a red shift up to 14 and 6 nm, respectively, with increasing solvent polarity. The polymers are highly soluble in ethanol with a solution photoluminescence quantum yield of 0.74. Polymer P2 in thin film cast from ethanol shows high intrachain order as revealed by red-shifted absorption spectrum and emission spectrum along with well-resolved vibronic structure. Both P1 and P2 are highly sensitive and selective Fe ³⁺ sensory materials, and the sensitivity is much higher than that of model compounds 3 and 4. The highest sensitivity was observed with polymer P1, and a 210-fold fluorescence quenching in dichloromethane was achieved. Polymer light-emitting diodes (PLEDs) were also fabricated to investigate the electroluminescent properties. A luminous efficiency of 1.49 cd/A with Commission Internationale de L'Eclairage (CIE) coordinates of (0.171, 0.131) at 100 cd/m² and a maximum brightness of 1750 cd/m² have been demonstrated.