A highly sensitive and selective Schiff-base probe as a colorimetric sensor for Co2+ and a fluorimetric sensor for F- and its utility in bio-imaging, molecular logic gate and real sample analysis.

In this work, we designed a novel Schiff-base probe from the condensation reaction of 3,5-diiodosalicylaldehyde with isoniazid. Treatment of the sensor molecule with different metal ions like K+, Ba2+, Ca2+, Mg2+, Fe2+, Mn2+, Co2+, Cu2+, Cd2+, Ni2+, Hg2+, Zn2+, Pb2+ and Al3+ in visual inspection and absorption measurements explained its colorimetric sensing ability. The sensor DISN displays a remarkable color variation from pale yellow to brownish-orange towards Co2+ ion. The absorption and emission spectra of DISN, upon treating with various anions including F-, Br-, Cl-, I-, HSO4-, NO3-, H2PO4-, and CN- were tested. The addition of the fluoride ion to the receptor caused not only the intense color variation from pale yellow to orange but also a significant fluorescence turn-on response. Job's plot method fixed the binding of Co2+ and F- to DISN separately, in 2:1 and 1:1 binding stoichiometry, respectively. The detection limit of 1.24 × 10-7 M and 0.108 × 10-6 M was attained for Co2+ and F-, respectively. The TD-DFT calculations further supported the photophysical properties involved in the free probe and its complexes. The YES and INHIBIT logic function was found to operate from modulation in the absorbance and fluorescence behavior of Co2+ and F- ions with DISN. Furthermore, DISN displays its practical applicability in filter-paper strips, live cell imaging, and real sample analyses.