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

Abstract

A highly selective and sensitive 2,7-naphthyridine based colorimetric, reversible, pH independent and fluorescence “Turn Off” chemosensors (L1-L4) for detection of Ni2+ are being reported in aqueous media. The synthesized sensors are highly efficient in detecting Ni2+ 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 Ni2+ with spectral changes in bands at 535–550 nm. The detection limit of Ni2+ for (L1-L4) are in the range of 0.2–0.5 µM which is 2–5 times lower than the permissible value of Ni2+ (1.2 µM) in drinking water defined by EPA. The binding mode of interactions of L1-L4 for Ni2+ were found to be 2:1 through job’s plot and ESI-MS analysis. Moreover the receptors can be used to quantify Ni2+ in real water samples and formation of test strips by dip-stick method increases the practical applicability of Ni2+ test for “in-the-field” measurement of Ni2+. Importantly the sensing potential of these derivatives have been tuned by the nature of substituents i.e. electron donating (CH3) and electron attracting (F, OCF3), which showed that L4 is highly efficient in sensing of Ni2+ even at minute level.