A phenothiazine-based "naked-eye" fluorescent probe for the dual detection of Hg²⁺ and Cu²⁺: Application as a solid state sensor

A phenothiazine-based colorimetric and fluorescent probe (3) for Hg²⁺ and Cu²⁺ was designed and synthesized. Probe 3 showed high selectivity and sensitivity toward Hg²⁺ and Cu²⁺ over other metal ions. This probe works as a chemodosimeter based on the Kucherov reaction for the selective detection of Hg²⁺. Copper recognition is based on soft-soft metal interactions with the -S and -N atoms of the probe 3. Probe 3 exhibited a red-shift in the absorption spectra from 449 to 606 nm for Hg²⁺ and at 612 nm for Cu²⁺ that is accompanied by significant color changes from orange to dark blue and blackish-blue. Probe 3 could be used as a solid state (test paper, TLC plates) optical sensor for the selective detection of Hg²⁺ and Cu²⁺. The binding process was confirmed by UV-vis absorption, fluorescence measurements, IR, ¹H NMR and mass spectroscopy.