An experimental and theoretical study of a new sensitive and selective Al3+ Schiff base fluorescent chemosensor bearing a homopiperazine moiety

Abstract

Schiff base ligands can be considered key to designing fluorescent chemosensors due to their chromogenic properties. Here, we study this view and demonstrate that there is a remarkable fluorescence enhancement upon Al3+ addition to a new macroacyclic Schiff base ligand (H2L) compared with 15 different metal ions, while the limit of detection (LOD) value is in good agreement with the values need for biological applications (2.1×10−9M). Besides, we show that it can be a satisfactory linear relationship between the gradually added concentrations of Al3+ and the fluorescence intensity of H2L. On the other hand, some transition shifts toward lower wavelengths were observed using the spectroscopic titration of H2L with Al3+ ions. From the theoretical point of view, NBO analysis revealed that the band gaps varied from 1.715 eV for H2L to 2.167 eV for [AlL]+, confirming the blue shift upon complexation. The high difference in band gaps approved the occurrence of a significant electrochemical signal. Furthermore, the nature of bonds in H2L and [AlL]+ was investigated by the QTAIM method specifying the shared property of bonds in H2L and the closed-shell metal-ligand interactions in [AlL]+. Ellipticity (ε) measurements indicated that the π-character of imine bonding decreased via complexation.