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.