Recognition of Fe3+ by a new azine-based fluorescent “turn-off” chemosensor and its binding mode analysis using DFT

Abstract

A highly responsible Fe3+, azine chemosensor (EBHMM) was successfully designed and synthesized. The structure of the synthesized azine was confirmed by FT-IR, UV–Vis, 1H and 13C{1H} NMR spectroscopic techniques and high resolution mass spectrometry. The azine shows sensitive and selective fluorescence “turn-off” towards Fe3+ ion over other metal ions in 1:1 DMF-H2O (5 μM, pH = 7.4) solution. The fluorescence quenching on the addition of Fe3+ ion at various pH clearly indicate that the azine can be used for the quantitative determination of Fe3+. The binding of Fe3+ with chemosensor was analyzed by confirming the formation of metal-ligand complex using HRMS-ESI spectrometry. The binding stoichiometry (1:1) was calculated using Stern-Volmer method and the binding constant 1.0034 M-1 was calculated using Benesi-Hildebrand plot. The exact binding sites of the chemosensor with Fe3+ ion is theoretically explained with Fukui Function using DFT study in B3LYP function with B3LYP/6-311++G (d,p) level of basis set. The “turn-off” fluorescence through photo induced electron transfer (PET) process is discussed and confirmed with the results of Fukui Function and Frontier molecular orbital analysis.