Multifaceted Chiral Probe 2,3-Dihydro-4-hydroxy-chromene Schiff Base in Detecting Cu2+ Ions, l‑Histidine, and Indazole: Spectroscopic Investigation and Confocal and Live Cell Imaging

2,3-Dihydro-4-hydroxy-chromene-4­(N)-ethyl thiosemicarbazone (probe F4) is used as a chemosensor, and it selectively detected Cu2+ ions among the metal ions by showing fluorescence "TURN ON" behavior. The stoichiometric binding of the probe with Cu2+ (CF4) was confirmed by Job’s plot and mass spectroscopy. Further, CF4 was used as a sensor for the detection of l-amino acids and N-heterocyclic compounds. Among them, CF4 selectively detected l-histidine by showing fluorescence “TURN-OFF” behavior and selectively detected indazole by showing fluorescence “TURN-ON” behavior. These behaviors were further confirmed by in vivo live cell imaging studies by using Caenorhabditis elegans as a model. In vitro cytotoxicity was assayed for probe F4, complex CF4, and CF4 with l-histidine and indazole. The IC50 concentration was used for confocal imaging studies by using the MDA-MB-231 cell line (breast cancer cell line).