Synthesis of a dihydroquinoline based fluorescent cyanine for selective, naked eye, and turn off detection of Fe3+ ions

A cyanine dye was synthesized by condensing 6-formylated 1,2,2,4-tetramethyl-1,2-dihydroquinoline (TMDQ) and 1,7-dimethyl-2-phenylimidazo[1,2-a]pyridin-1-ium iodide. The probe was a selective sensor for ferric ions in aqueous ethanolic solution. The sensor was fluorescent and the fluorescence was quenched by Fe3+ ions. The decrease in the fluorescence was quick and linear with respect to Fe3+ ions. The quenching was selective and no other metal ions tested showed this effect. The colour change could be detected visually and hence it is a naked eye and turn-off fluorescence detector for Fe3+ ions.