Dehydro acetic acid analogue Schiff base as multimode fluorescence chemosensors for Th4+ and Ni2+ ions and its application to in-vivo bioimaging

Dehydroacetic acid analogue (DHA) and 7-(diethylamino)-2-oxo-2H-chromene-3-carbohydrazide (COM) Schiff base ligand (COM-DHA) as dual-mode fluorescence chemosensor was synthesized and structurally characterised by using elemental analysis, FTIR, NMR, and Mass analysis. The free probe COM-DHA shows distinct fluorescence emission at 476 nm, upon interaction with Ni²⁺ the emission intensity was quenched and with Th⁴⁺ the emission intensity was redshirted to 500 nm. Further, the ratiometric fluorescence change (I₅₀₀/I₄₇₆) was used to detect Th⁴⁺, and a turn-off fluorescence probe COM-DHA at 476 nm was used to detect Ni²⁺ ions. The COM-DHA forms a 2:1 stoichiometric complex with both Ni²⁺/Th⁴⁺ ions with an estimated association constant of 4.84 × 10⁴ and 6.68 × 10⁴ M⁻² respectively. A further probe COM-DHA is that it has a wide working pH range (5 to 10) with a short response time (2 to 3 min). The detection limit of COM-DHA towards Ni²⁺ and Th⁴⁺ was found to be 77.8 and 48.7 nM, respectively. The, DFT/TD-DFT calculations and FTIR analysis were used to study the binding mechanism between COM-DAH and Ni²⁺/Th⁴⁺ ions. Furthermore, the proposed probe COM-DHA has successfully quantified trace amounts of Ni²⁺ and Th⁴⁺ in real samples and applied them to the in-vivo bioimaging of Th⁴⁺ in C. elegans model.