Carboxylated ‘locking unit’ directed ratiometric probe design, synthesis and application in selective recognition of Fe3+/Cu2+

Abstract

A ratiometric probe has been designed and synthesized through the introduction of a carboxylated functionality. The probe 1, synthesized in two steps, was found to be a fluorescent chemosensor for the selective ratiometric detection of Fe³⁺/Cu²⁺ over a wide range of metal ions quite efficiently. The carboxylated unit, ‘CH₂COOH’, acts as a ‘locking unit’ restricting the possibility of E/Z isomerization and ESPT. This has been supported by theoretical studies. The selectivity was established using various spectroscopic techniques such as UV-vis and fluorescence spectroscopy. The probe was found to have fluorescence properties with a quantum yield of 0.18. The binding of this fluorescent receptor to metal ions was also proved by NMR and mass spectrometry. The present probe can efficiently detect the presence of very low concentrations of Fe³⁺/Cu²⁺ (0.51 and 4.46 μM of Cu²⁺ and Fe³⁺ respectively).