A hydroxypropiophenone-based fluorescent probe for the selective determination of Al(III) ions in aqueous ethanol

In this work, we have synthesized a novel dihydrazone-based fluorescent probe N'1,N'2-bis{1-(2-hydroxyphenyl)propylidene}oxalohydrazide (H2hpoh)for Al3+ ions by a simple condensation reaction. The prepared organic probe has been characterized by different physicochemical and spectroscopic techniques. The single-crystal structure of the receptor has also been reported. Crystal data for C20H22N4O4: monoclinic, space group P21/c (no. 14), a = 6.0747(15) Å, b = 11.621(5) Å, c = 13.453(4) Å, β = 94.61(3)°, V = 946.6(5) Å3, Z = 2, T = 293(2) K, μ(MoKα) = 0.096 mm-1, Dcalc = 1.342 g/cm3, 4046 reflections measured (6.076° ≤ 2Θ ≤ 58.05°), 2149 unique (Rint = 0.0876, Rsigma = 0.2223) which were used in all calculations. The final R1 was 0.0972 (I > 2σ(I)) and wR2 was 0.2316 (all data). The ethanolic aqueous solution of the probe shows enhanced fluorescence in the presence of Al3+ ions, whereas no appreciable change in the spectral pattern is observed in the presence of other cations, i.e., Na+, K+, Ca2+, Ba2+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Cr3+, Cd2+ and Hg2+. The binding mode of the receptor with Al3+ ions was studied using various spectral titration techniques such as UV-visible, fluorescence, and 1H NMR. The receptor acts as a dibasic hexadentate ligand and interacts with two Al3+ ions with a high binding constant KB = 8.99×1010 1/M. The lowest detection limit for the Al3+ complex of H2hpoh was determined to be 7.8×10−5 M. With the help of DFT calculations, the mechanism of fluorescence enhancement has been explained.