Naked eye sensing of toxic metal ions in aqueous medium using thiophene-based ligands and its application in living cells

Thiophene-based diimine (R1) and monoimine (R2) were synthesized in a single step, and their cation binding affinity was tested using colorimetric and UV-vis spectral studies. R1 selectively shows a colorimetric turn-on response for Pb(2+), Hg(2+) ions and colorimetric turn-off with Sn(2+) ions, and R2 shows visual response for Cu(2+) and Hg(2+) over other examined metal ions in aqueous medium. R1 forms 1:1 complex with Pb(2+), Hg(2+), and Sn(2+) and exhibits fluorescence quenching, whereas R2 shows 2:1 complex with Hg(2+), Cu(2+) and shows fluorescence enhancement. The structural and electronic properties of the sensors and their metal complexes were also investigated using Density Functional Theory calculations. R2 was also successfully demonstrated as a fluorescent probe for detecting Cu(2+) ions in living cells.