Turn-on fluorescent detection of nickel and zinc ions by two related chemosensors containing naphthalimide ring(s)

•Two chemosensors are presented that are conjugated with naphthalimide ring(s).•Both chemosensors act as the “Turn-on” fluorescent sensors for the detection of Ni2+ and Zn2+ ions.•Job's plot and high-resolution mass spectra established a 1:1 stoichiometry of chemosensors with Ni2+ and Zn2+ ions.•DFT studies and HOMO-LUMO calculations further established a 1:1 stoichiometry.•Colorimetric sensing, paper test-strips and polystyrene films are used for the sensing of Ni2+ and Zn2+ ions in aqueous solutions.