A novel light-emitting monomer M1 and its side-chain polymer P1 containing three conjugated aromatic pendants, including one pyridyl terminus, were successfully synthesized via Wittig and Pd-catalyzed Heck coupling reactions. The fluorescence of polymer P1 was efficiently quenched upon addition of different metal ions due to the facile energy transfers from the pendent groups of polymer P1 to specific metal ions. Among these metal ions, P1 exhibited extraordinary sensory selectivities for Ni2+ and Cu2+ ions over the other metal ions due to the stronger binding capabilities of Ni 2+ and Cu2+ ions with polymer P1. From the time-resolved fluorescence (TRF) signals in photoluminescence spectra, the emergences of τ1 decay components in polymer complexes (P1+Ni2+) and (P1+Cu2+) clearly indicated that their TRF traces consisted of two contributions, one from the complexes (τ1) and the other from free polymer P1 (τ2). Upon addition of Ni2+ and Cu2+ ions, polymer P1 showed faster decay time constants (τ1) of metal ion quenching on TRF signals (i.e., better quenching efficiencies on photoluminescence) than its monomer M1. Furthermore, the on-off-on fluorescent switching behavior by adding a tridentate ligand 1,1,4,7,7-pentamethyldiethylenetriamine (PMDTA) to the polymer complex (P1+Cu2+) for several successive cycles demonstrated a superior reusable chemosensor of P1 for further applications.