Spirolactam capped cyanine dyes for designing NIR probes to target multiple metal ions

A cyanine based spirocyclic metal ion probe has been reported, which can be tuned easily for targeting various metal ions. The mechanism of selective sensing was verified by designing two novel compounds IR-NCS and IR-PYR, which can selectively sense Hg²⁺ and Zn²⁺/Cd²⁺ ions respectively in a mixed aqueous medium and physiological pH. The spectral changes in both the cases are in the near infrared (NIR) region. Both chemodosimetric and coordination based approaches were used for sensing the cations. The complete mechanism of the sensing events was studied using UV-Vis and fluorescence spectroscopy. Additional insight about the experimental findings was corroborated by theoretical studies using DFT calculations. The confocal microscopic study revealed that the probe IR-NCS can be effectively used for detecting intracellular levels of Hg²⁺ ions without showing any toxic effect to the model human cells.