Spectroscopic and TD-DFT studies on sequential fluorescent detection of Cu(II) and HS- ions in an aqueous solution

[Display omitted] •The fluorescent probe AK1 sequentially sensed of Cu(II) and HS- ions via OFF-ON mechanism.•Job’s plot, mass, FT-IR and EPR spectral data indicated formation of distorted octahedral [(AK1)2Cl(H2O)Cu] complex.•The LOD of AK1 for Cu(II) was 18 µM.•DFT and TD-DFT calculations strongly supported the optical experimental results. A new highly selective fluorescent probe AK1 was designed, synthesized and characterized, by conventional techniques, including single crystal XRD analysis, for sequential sensing of Cu(II) and HS- ions in an aqueous solution. The probe showed significant fluorescence quenching in the presence of Cu(II), while other metal ions produced only minor changes in the fluorescence of AK1. Job’s plot and mass and EPR spectral analyses indicated a 2:1 binding stoichiometry between AK1 and Cu(II) ions. The limit of detection (LOD) of AK1 for Cu(II) was determined to be 7.7 µM, which is far lower than the USEPA limit (∼20 µM) for drinking water. Subsequently, the in situ generated AK1-Cu(II) complex acts as a highly selective and sensitive probe for HS- ion, with an enhancement in fluorescence, even in the presence of different anions. Notably, the probe could detect and quantify Cu(II) and HS- ions in real water samples. Moreover, the optical properties of the probe in the absence and presence of Cu(II) and HS- ions were explained by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations.