2,7-Naphthyridine based colorimetric and fluorescent “Turn Off” chemosensors for selective detection of Ni(II) in aqueous media

A highly selective and sensitive 2,7-naphthyridine based colorimetric, reversible, pH independent and fluorescence “Turn Off” chemosensors (L1-L4) for detection of Ni 2+ are being reported in aqueous media. The synthesized sensors are highly efficient in detecting Ni 2+ even in the presence of other metal ions that commonly co-exist with nickel. The receptors (L1-L4) showed a distinct color change from yellow to red by addition of Ni 2+ with spectral changes in bands at 535–550 nm. The detection limit of Ni 2+ for (L1-L4) are in the range of 0.2–0.5 µM which is 2–5 times lower than the permissible value of Ni 2+ (1.2 µM) in drinking water defined by EPA. The binding mode of interactions of L1-L4 for Ni 2+ were found to be 2:1 through job’s plot and ESI-MS analysis. Moreover the receptors can be used to quantify Ni 2+ in real water samples and formation of test strips by dip-stick method increases the practical applicability of Ni 2+ test for “in-the-field” measurement of Ni 2+ . Importantly the sensing potential of these derivatives have been tuned by the nature of substituents i.e. electron donating (CH 3 ) and electron attracting (F, OCF 3 ), which showed that L4 is highly efficient in sensing of Ni 2+ even at minute level.