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

Schiff base ligands can be considered key to designing fluorescent chemosensors due to their chro-mogenic 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 dif-ferent metal ions, while the limit of detection (LOD) value is in good agreement with the values need for biological applications ( 2 . 1 x 1 0 -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 var-ied 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 prop-erty of bonds in H2L and the closed-shell metal-ligand interactions in [AlL]+. Ellipticity (epsilon) measurements indicated that the pi-character of imine bonding decreased via complexation.(c) 2022 Published by Elsevier B.V.