Pyridine-containing polyenes and their applications as metal ion sensors. These polyenes are practically nonluminescent in the solution state but become highly emissive as nanoparticle suspensions in aqueous solutions or thin films in the solid state, due to aggregation-induced emission (AIE). The nanoaggregates of these compounds can work as “turn-off” fluorescent chemosensors for metal ions and display different fluorescence responses to various metal ions. For example, a characteristic red shift in the emission spectra is observed with a terpyridine-containing luminogen in the presence of Zn2+. However, the terpyridine-containing luminogen displays a magenta color upon selectively binding with Fe2+. This allows easy identification of both Zn2+ and Fe2+ ions in aqueous media. The function of the polyenes can be easily tuned by altering the substituent groups. Due to their AIE properties, these polyenes can be used in aqueous solutions and in solid substrates for metal sensing.