Highly sensitive fluorescence turn-OFF and reversible chemical sensor for Hg2+ ion based on pyrene appended 2-thiohydantoin.

A novel fluorometric chemical sensor (PY-2TH) based on 2-thiohydantoin (2TH) in conjugation with pyrene (PY) was designed by facile one-pot Knoevenagel condensation reaction and explored for the sensitive and selective detection of Hg2+ ion in solution and solid state methods. Different analytical techniques like NMR and LC-MS concomitantly confirmed the structure of PY-2TH. Absorption and emission studies demonstrate positive solvatochromic effects indicating intramolecular charge transfer in polar solvents. PY-2TH exhibits unprecedented selectivity for detecting Hg2+ ions in tetrahydrofuran (THF) through turn-OFF fluorescence with 90% decrease in the emission intensity with a limit of detection (LOD) of ∼4.4 ppb. The mechanistic investigation through NMR and optical studies confirm the formation of a 2:1 complex between PY-2TH and Hg2+. Thin films of PY-2TH exhibits the J-aggregate formation in the solid state leading to a shift in the emission towards the near-infrared region. Further, we have demonstrated the applicability of PY-2TH for detection of Hg2+ ions and fluorescence imaging in live Zebrafish larvae and the toxicological effects are explored. Cytotoxic evaluation on Zebrafish larval cells revealed that PY-2TH is found to be non-toxic. Detailed analysis demonstrate the potential of PY-2TH for ultra-sensitive Hg2+ ion detection and removal in aqueous environments, highlighting its applicability for identification of metal contamination in live organisms and environmental toxicity.

Fluoranthene-terminated terpyridine ensemble for fluorescence light up and ratiometric chemical sensor for multi toxic metals.

A novel π-electron rich fluoranthene embellished with a phenyl spacer and coupled with terpyridine (TS1) was developed through Diels-Alder reaction. Single crystal X-ray structure evidences the variations in dihedral angles between the fluoranthene and the phenyl unit responsible for development of non-coplanar interactions and stabilized by a wave-like molecular packing in the crystal lattice with weak π-π interaction of 4.125 Å. The peripheral terpyridine of TS1 endows an efficient binding with multiple metal ions by colorimetric and fluorometric methods. TS1 exhibits a ratiometric fluorescence response from sky blue to yellow colour upon the addition of Zn2+ ions with a limit of detection (LOD) of 0.05 ppm. The other metal ions such as Cu2+, Co2+ and Fe2+ demonstrate fluorescence quenching behaviour with LODs of 0.1, 0.3 and 0.7 ppm, respectively. The intramolecular charge transfer (ICT) shows the variation in TS1 emission behaviour upon metal ions interaction and quantitatively discriminates the metal ion concentrations. TS1 conferred a visual colorimetric change from colourless to magenta, enabling naked-eye detection of Fe2+ and showing clear discrimination between Fe2+ and Fe3+ ions for the real-time water samples. Furthermore, we have investigated the effect of TS1 in Zebrafish larvae/embryos and cytotoxicity in human urinary tract transitional cell carcinoma cells (UM-UC-3).