Hydrazone based luminescent receptors for fluorescent sensing of Cu2+: Structure and spectroscopy

Two new luminescent hydrazones, HL1 and HL2 were investigated for selective and sensitive fluorescent recognition of Cu2+ in aqueous medium (CH3CN/H2O (1:4, v/v) solvent system) with a 1:1 binding stoichiometry. The emission peak of HL (λem=405 nm), undergoes significant quenching upon complexation with Cu2+. The quantum yields for the receptors and in situ formed Cu2+ complexes were determined. The absorption ratiometric analysis was carried out in presence of various metal ions to confirm the selectivity of the receptors towards Cu2+. They were able to detect Cu2+ with a ~0.9 µM detection limit as indicated by fluorimetric measurements. The molecular structures of the receptors were determined by single crystal X-ray diffraction analysis.