Bis(2-pyridylmethyl)amine-functionalized alizarin: an efficient and simple colorimetric sensor for fluoride and a fluorescence turn-on sensor for Al3+ in an organic solution.

A complexone analog chemosensor, H2L, bearing chelating bis(2-pyridylmethyl) amine and alizarin groups was synthesized via the Mannich reaction. H2L chromically responds to OH−, F−, CH3COO−, and H2PO4− in DMF, CH3CN, and acetone, but not in CH3OH or H2O. The addition of F− ions to H2L selectively induces a significant and visible color change in acetonitrile and shifts both methylene proton signals upfield. H2L also exhibits visible responses to Mg2+, Sr2+, Ba2+, Tb3+, Cu2+, Co2+, Ni2+, Zn2+, Mn2+, Cd2+, and Fe3+ in solution. AlCl3 can form an Al : L = 2 : 3 complex that not only changes the color of the DMF solution, but also significantly increases its fluorescence intensity. The limit of fluorescence turn-on detection for AlCl3 in DMF is 2.7 × 10−8 M, which is an order higher than those of other anthraquinone sensors reported in the literature. NMR spectroscopy shows that hydroxyl is not deprotonated upon interacting with Al3+, but will be partially deprotonated in the presence of Zn2+. Contrary to the complexone, the H2L–Ce(iii) complex does not react chromically to F−. However, the H2L–NiCl2 complex responds chromically to F−, with higher sensitivity (LOD = 1.3 × 10−6 M F− in acetonitrile) than free H2L. The spectral changes in the presence of F− are similar to that of OH−; however, the spectrum shifts slightly to a longer wavelength and is more sensitive to both H2L and the H2L–NiCl2 complex. Moreover, 4% or less H2O in the solvent essentially has no influence on the F− sensitivity; however, high water content significantly decreases the F− sensitivity. The spectral changes of the Zn2+, Cu2+, Fe3+, Ce3+, and Ni2+ complexes in the presence of different NaOH concentrations were also investigated. [ABSTRACT FROM AUTHOR]