N-diethylaminosalicylidene based "turn-on" fluorescent Schiff base chemosensor for Al3+ ion: Synthesis, characterisation and DFT/TD-DFT studies.

• The chemosensor (H 3 L) showed high selectivity for Al3+ ion. • The binding ratio of H 3 L:Al3+ was obtained as 2:1 determined by the Job's plot and 1H NMR titration in solution phase. • DFT/TD-DFT calculations showed the stability of Al3+–complex. • The DFT/TD-DFT values for emission and electronic studies show good agreement with experimental values. A Schiff base chemosensor (H 3 L) based on the 4-(N,N-Diethylamino)salicylaldehyde moiety has been synthesized and characterized using several spectroscopic techniques i.e. 1H-NMR, FT-IR, Mass and UV-visible. The chemosensor shows high selectivity for Al3+ ion through 'turn-on' cyan colour fluorescence over a variety of metal ions i.e. Ni2+, Zn2+, Cd2+, Mn2+ ions except Co2+, Cu2+ and Fe3+ ions. The chemosensor exhibits 20 fold intensity enhancement at 481 nm (λ ex = 378 nm) against Al3+ ion until saturation point. Additionally, the detection limit and stability constant were found to be 1.2 × 10−6 M and 5.2 × 105 M−1, respectively with the low equivalent range of 1–34 µM. The chemosensor also displays similar fluorescence behaviour for Al3+ ion in a variety of solvents and solvent mixtures. The quantum yield (Ф F) values for H 3 L and Al3+–complex were observed to be 0.08 and 0.29, respectively. The Job's plot calculations show that, H 3 L binds to Al3+ ion in 2:1 ratio. 1H-NMR titration analysis indicates that the chemosensor undergoes mono-deprotonation while binding to Al3+ ion. The geometry of the chemosensor and Al3+–complex were optimised and some thermodynamic parameters were calculated using Density Functional Theory (DFT). The Gibbs free energy of complex was calculated to be -1272.00 kcal/mol. Further, the optical and electronic properties of the proposed complex were explained with the help of Time Dependent-Density Functional Theory (TD–DFT). [Display omitted] [ABSTRACT FROM AUTHOR]