Fluorescence "Turn-Off" and Colorimetric Sensor for Fe(2+), Fe(3+), and Cu(2+) Ions Based on a 2,5,7-Triarylimidazopyridine Scaffold.

Two cyanoimidazopyridine-based sensors (SS1 and SS2) were explored for the colorimetric and fluorometric detection of Fe(2+), Fe(3+), and Cu(2+) ions in the semi-aqueous medium. The "turn-off" fluorescence response of both sensors to these ions was due to the restriction in internal charge transfer. Job's plot and semi-empirical calculations revealed that SS1 and SS2 complexed with Cu(2+) ions in a 1:1 ratio and Fe(2+/3+) ions in a 2:1 ratio, respectively. The sensors were found to have high binding constant (K (a)) values and low detection limit values. FMO analysis using the semi-empirical quantum mechanics method revealed the decrease in energy gap after complexation with metal ions. Sensor-coated filter paper strips were prepared and analyzed, where the color changes in the strips could be utilized for the real-time detection of Fe(2+), Fe(3+), and Cu(2+) ions.