Dual sensing and synchronous fluorescence spectroscopic monitoring of Cr³⁺and Al³⁺ using a luminescent Schiff base: Extraction and DFT studies

A well designed, new pyrene based small molecule (L) was synthesized from 1:1 condensation reaction of 1-aminopyrene and 6-(1,3-benzodioxal-5-yl)-2-pyridine carboxaldehyde which was characterized by absorption, emission spectrometry, FTIR, NMR and mass studies. Interestingly the UV-vis and fluorescence spectroscopic studies revealed that the ligand (L) works as a dual turn-on luminescent chemosensor for chromium(III) (Cr³⁺) and aluminium(III) (Al³⁺) in aqueous environment which were further supported by DFT and TDDFT studies. L shows a significant colour change from pale yellow to reddish yellow with a detection limit of ~10^-9 M in the presence of Cr³⁺ and Al³⁺ whereas there were no noteworthy changes in the presence of other monovalent and divalent metal ions. The molecular signaling in the presence of Cr³⁺, Al³⁺, Fe³⁺ and EDTA was compared with advanced level combinational INHIBIT gate based on 4 input logic gates. Herein, first derivative constant wavelength synchronous fluorescence spectroscopy (1^st DCWSFS) was applied for the determination of Cr³⁺, Al³⁺ ion concentrations in a mixture via increment of spectral resolution of the respective overlapping peaks. 1^st DCWSFS is reported to be used in pharmaceuticals but very few works have been done for determination of metal ion concentration in environmental sample without prior separation. The individual Cr³⁺and Al³⁺ ion concentrations in a mixture were determined through liquid-liquid extraction process and the efficiencies were compared with 1^st derivative SFS method. It was observed that 1^st derivative SFS process is more efficient than conventional liquid-liquid extraction process. Therefore, 1^st DCWSFS method using sensor L might be useful as a diagnostic tool for detection of individual metal ion concentrations (Cr³⁺ and Al³⁺) from a mixture which will be cost-effective, time saving and more precise.