Naphthyridine derived colorimetric and fluorescent turn off sensors for Ni2+ in aqueous media
Abida Ashraf, Muhammad Islam, Muhammad Khalid, Anthony P. Davis, Muhammad Tayyeb Ahsan, Muhammad Yaqub, Asad Syed, Abdallah M. Elgorban, Ali H. Bahkali, Zahid Shafiq
Abstract
Abstract Highly selective and sensitive 2,7-naphthyridine based colorimetric and fluorescence “Turn Off” chemosensors (L1-L4) for detection of Ni 2+ in aqueous media are reported. 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 changes are reversible and pH independent. The detection limits for Ni 2+ by (L1-L4) are in the range of 0.2–0.5 µM by UV–Visible data and 0.040–0.47 µM by fluorescence data, which is lower than the permissible value of Ni 2+ (1.2 µM) in drinking water defined by EPA. The binding stoichiometries 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. Formation of test strips by the dip-stick method increases the practical applicability of the Ni 2+ test for “in-the-field” measurements. DFT calculations and AIM analyses supported the experimentally determined 2:1 stoichiometries of complexation. TD-DFT calculations were performed which showed slightly decreased FMO energy gaps due to ligand–metal charge transfer (LMCT).