Phenyl-end-capped-thiophene (P-T type) based ICT fluorescent probe (D–π–A) for detection of Hg2+ and Cu2+ ions: Live cell imaging and logic operation at molecular level

• Photophysical behavior of a ratiometric probe BTIM has been described.
• It shows fluorescence turn-on (D–π–A type) response upon interaction with Hg2+ and Turn-Off response with Cu2+ in solution and living cell.
• Optical behavior has been utilized for logic operation at molecular level.

An intramolecular charge transfer (ICT) based fluorescence turn-on ratiometric probe BTIM (D–π–A type) has been designed and synthesized by bridging imidazole (donor, D) and benzothiazole (acceptor, A) moieties through a thiophene ring. The photophysical behavior of probe and its affinity toward metal ions has been investigated in HEPES buffer, protein medium and live cells. The probe upon interaction with different cations has shown high sensitivity and selectively for Hg2+ and Cu2+ ions through fluorescence “turn-On and turn-Off” response respectively along with naked-eye sensitive color changes. The significant change in photophysical behavior of the probe is attributable to restricted ICT upon complexation between probe and metal ions in a 1:1 stoichiometry. The mechanism of interaction has been established by 1H NMR, FT-IR, ESI-M Sand DFT calculation methods. The probe has shown excellent cell permeability and successfully detected Hg2+ and Cu2+ ions in Dalton’s Lymphoma (DL) cells, in protein medium (BSA), in real water samples and on test paper strips. Moreover, the optical behavior of probe has been explored as a Coding-Decoding Fluorescent Blue Security Ink on silica gel surface and in construction of crossword puzzle with specific security code ‘HCO’.

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