Antipyrine based Schiff's base as a reversible fluorescence turn "off-on-off" chemosensor for sequential recognition of Al3+ and F- ions: A theoretical and experimental perspective.

Abstract

A Schiff's base probe (L) based on antipyrine has been intended, synthesized and assessed as a turn "off-on-off" probe for successive recognition of Al3+ and F-. The probe L act out as a turn "on" fluorescence probe towards Al3+ in methanol at pH 6 which turned "off" by F- at 433 nm. The 1:1 binding stoichiometry of L +Al3+ complex was revealed by Job's plot and approved by ESI-HRMS data. The binding constant and limit of detection of probe L for Al3+ were found to be 2.951 × 107 M-1 and 0.61 × 10-7 M respectively, which is lesser than the acceptable limit (0.74 × 10-7 M) in drinking water. The proposed binding sites and the mode of interaction of probe L was studied and validated by 1H NMR titration and 27Al NMR spectroscopic studies. To get detailed vision into binding mechanism and optimized structure of receptor L and L +Al3+, L +Al3++F- complex, theoretical calculations using DFT/DND and TDDFT method were performed. Furthermore, probe L can mimic INHIBIT logic function using Al3+ and F- being logic inputs and examining the fluorescence maxima at 433 nm as output.