Terpyridine Functionalized Oligothiophene: Cadmium(II) Ion Sensing via Visualization and Fluorescence

Abstract

Abstract2,2′:6′,2′′‐Terpyridine functionalized terthiophene (3T‐Terpy) has been explored and its sensing behaviors toward various metal ions have been investigated. It was found that presence of Cd2+ causes a remarkable variation in the absorption and more than 65 nm red shift of the maximum fluorescence emission of the compound, corresponding to a visual green to yellow color change under UV light. Other commonly found transition metal ions exhibit different interference even though some of them, Cu2+, Co2+ and Ni2+ as examples, may quench the emission of the fluorophore. Similar to that of Cd2+, presence of Zn2+ or Hg2+ also alters the color of the methanol solution of 3T‐Terpy, but the colors of them are different. The detection limit for Cd2+ based on the mechanism of intramolecular charge transfer was found to be around 1.74 × 10−7 M. Addition of other main group metal ions (e. g., Na+, K+, Mg2+ and Ba2+) shows little effect to the fluorescence emission. Job's plot reveals formation of a 2:1 complex between 3T‐Terpy and Cd2+ with a binding constant of 2.25 × 105 M−1 and the dynamic metal‐ligand coordination can be recovered by adding EDTA. Furthermore, the change in fluorescence of 3T‐Terpy loaded test strips upon contact with Cd2+ can be clearly observed by the naked eyes with the aid of a portable UV lamp. Therefore, excellence in sensing and simplicity in structure make 3T‐Terpy a superior fluorescent chemosensor of the relevant transition metal ions, in particular Cd2+.