Nitroquinolone Fused Salicyl and Naphthyl Hydrazone Fluorescent Probes for the Detection of Fe3+and Pb2+ Ions.

The application of quinolones stretches over a large umbrella of medicinal field as well as chemosensor due to the presence of privileged heterocyclic aromatic rig system. Salicyl and Naphthyl Hydrazide motifs are also established fluorophore groups. Therefore in this work, we have designed and synthesized Salicyl hydrazide (3a-c) and naphthyl hydrazide fused nitroquinolones (5a-c) investigated for their fluorescent behaviour. Preliminary UV- absorption studies were carried out and the metal selectivity were examined with various metal ion. Among them, it was found that compound 3a was selective towards Fe³⁺ ions (λ_ex = 330 nm, 1:1 DMF:H₂O at pH = 7.4 in HEPES Buffer medium). 3a shows decrease emission intensity in presence of Fe³⁺ ions. Compound 5a shows enhancement in fluorescence intensity upon addition of Pb²⁺ ion (λ_ex = 280 nm, 1:1 DMF:H₂O at pH = 7.4 in HEPES Buffer medium). Further, the concentration dependence, competitive binding and EDTA reversibility were studied for selected compounds towards the respective cations selectivity. Jobs plot analysis indicate that 1:1 binding of 3a with Fe³⁺ ion (K_a = 3.17 x10⁴M^-1 and Limit Of Detection (LOD) = 5.1 × 10^-7 M) whereas 5a showed 1:2 binding mode with Pb²⁺ ions (K_a = 2.14 × 10⁶ M^-1 and Limit Of Detection (LOD) = 2.613 × 10^-9 M). Density Function Theoretical studies were performed as support for the experimental results.