Multi-Step Synthesis, Characterization and Physicochemical Investigation of Benzylated Indole Thiosemicarbazone as Selective Switch on Sensing Properties for Copper Ion.

A selective and specific Fluorescent chemosenor benzyl-indole-based thiosemicarbazone (BMP), was synthesized via the condensation between benzylated indole and phenylthiosemicarbazide as depicted in (Scheme 3). The compound BMP structure was confirmed by Mass spectrometry, IR, and 1H-NMR and 13C-NMR spectral techniques. The solvent interaction between BMP and various solvents were investigated by UV-vis and fluorescence titration studies, revealing a bathochromic shift (red shift) in the absorption and emission spectra, because of solvent polarity dependency. The selectivity and specificity of BMP for the identification of Cu (II) ion was examined by fluorescence spectrometry titration. The results demonstrated that upon the addition of 0.5 × 10-2 M of aqueous Cu2+ ions solution to the 0.1 × 10-3 M of BMP in acetonitrile, a noticeable enhancing of fluorescence was observed. The fluorescence enhancing mechanism was analyzed using various photophysical approaches, including spectroscopic titration, Benesi-Hildebrand analysis, Job's plot graph, and confirming a 1:1 stoichiometry ratio between BMP and Cu2+ ions. The association constant (Ka) of BMP for Cu2+ ions was determined to be 1.83 × 104 M-1.