Fluorogenic Zn(II) and Chromogenic Fe(II) Sensors Based on Terpyridine-Substituted Tetraphenylethenes with Aggregation-Induced Emission Characteristics

Terpyrkline-containing tetraphenylethenes (TPEs) are synthesized and their optical and metal sensing properties are investigated. They are practically nonluminescent in the solution state but become highly emissive as nanoparticle suspensions in poor solvents or thin films in the solid state, demonstrating a novel phenomenon of aggregation-induced emission (ME). The emission of the nanoaggregates of TPEs is pH-sensitive: it is decreased and eventually quenched upon protonation of their terpyridine units because of their AIE nature. The TPEs can work as turn-off fluorescent chemosensors for metal ions and display different fluorescence responses to various metal ions. A characteristic red shift in the emission spectra is observed in the presence of Zn2+, which facilitates the discrimination of Zn2+ from other metal ions. Because of the metal-to-ligand-charge-transfer process, terpridine-substituted TPEs display an obvious magenta color upon selectively binding with Fe2+, allowing a rapid identification of Fe2+ in the aqueous media by naked, eyes.