Isoquinoline-Fused Benzimidazoles Based Highly Selective Fluorogenic Receptors for Detection of Cu2+, Fe3+, and Cl− Ions: Cytotoxicity and HepG2 Cancer Cell Imaging

An efficient isoquinoline-fused benzimidazole–based “turn-on” fluorescence receptor 9,10-bis(2-phenylhydrazineyl)-7H-benzo[de]imidazo[2,1-a]isoquinolin-7-one OXPH(ANQ) and “turn-off” fluorescence receptor 9,10-bis((3-(1H-imidazol-1-yl)propyl)amino)-7H-benzo[de]imidazo[2,1-a]isoquinolin-7-one OXPID(ANQ) were prepared and characterized by various spectral techniques. The sensing behavior of receptors was demonstrated by UV–vis and fluorescence experiments, and naked-eye detection exhibited prominent visual emission color change toward Cu²⁺/Cl⁻ and Fe³⁺ over other testing cations/anions in DMSO:water (9:1, ν/v) solution. The 1:1 binding stoichiometry was confirmed by Job's plot, FT-IR, mass spectral titration, and also DFT studies with target ions as evidence for the binding nature of OXPH(ANQ)/OXPID(ANQ) with Cu²⁺/Cl⁻ and Fe³⁺ ions, respectively. Limits of detection for OXPH(ANQ) with Cu²⁺/Cl⁻ ions were of 4.50 and 4.91 μM, and OXPID(ANQ) with Fe³⁺ ions were of 5.06 μM. Interestingly, chemosensors OXPH(ANQ)/OXPID(ANQ) applied to intracellular image of Cu²⁺/Cl⁻ and Fe³⁺ ions in living cells of HepG2 (Liver cancer cells) via confocal fluorescence microscopy technique at physiological environmental and also utilized for antimicrobial activity.