This paper describes the synthesis of a triphenylamine-substituted alternating conjugated polyfluorene (PFAD) containing a pendant terminal di(2-picolyl)amine (DPA) group through the Heck coupling reaction. We examined the effect of DPA units on the sensory characteristics of fluorescent chemosensors. Photoluminescence titrations demonstrated that PFAD exhibited high sensitivity to Fe³⁺ ions. Furthermore, in a solution of tetrahydrofuran and water, a remarkable change was observed in the fluorescence color of PFAD, which had a Stern–Volmer constant of 1.30 × 10³ M⁻¹, from bright blue to dark upon adding Fe³⁺ ions. Because of the considerably high stability constant of the CN⁻–Fe³⁺ complex, the fluorescence of the PFAD solution that was quenched by Fe³⁺ ions recovered upon the addition of trace CN⁻ anions; the detection limit was as low as 1.08 × 10⁻⁵ mol l⁻¹. PFAD exhibited a high fluorescence quantum yield (0.73), suggesting that it is a promising material for use in polymeric light-emitting diodes and as a chemosensor.