Fluorescence sensing of metal ions in solution using a morpholine-containing phenolic Mannich base of 1'-hydroxy-2'-acetonaphthone.

A phenolic Mannich base derived from 1'-hydroxy-2'-acetonaphthone (HAN) as a substrate and morpholine as an amine reagent was synthesized and structurally characterized. The sensing ability toward various metal ions of the s-, p- and d-block of this molecule that has the binding site for metal ions in the starting -hydroxyphenone preserved was examined. Interaction between this phenolic Mannich base and Al, Cr, Cu and Co leads to modifications of the sensing molecule's absorption spectrum. Fluorescence spectroscopy showed that Al acts as a fluorescence enhancer, whereas Cu functions as a fluorescence quencher for the aminomethylated derivative. The phenolic Mannich base may be employed either as a sensitive "turn-on" chemosensor for Al or as a sensitive "turn-off" chemosensor for Cu. However, in the presence of these ions at identical concentrations, the Mannich base becomes a selective chemosensor for Al. The sensing ability of this phenolic Mannich base toward rare earth ions showed that Eu, Dy and Gd induce changes in the absorption spectrum of the Mannich base. Fluorescence spectroscopy showed that the response of the sensing molecule toward Eu and Dy is weak, and this phenolic Mannich base may be used as a "turn-off" chemosensor for these two lanthanide ions only in a narrow concentration range (1-16 × 10 M).