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 ortho -hydroxyphenone preserved was examined. Interaction between this phenolic Mannich base and Al 3+ , Cr 3+ , Cu 2+ and Co 2+ leads to modifications of the sensing molecule's absorption spectrum. Fluorescence spectroscopy showed that Al 3+ acts as a fluorescence enhancer, whereas Cu 2+ 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 3+ or as a sensitive "turn-off" chemosensor for Cu 2+ . However, in the presence of these ions at identical concentrations, the Mannich base becomes a selective chemosensor for Al 3+ . The sensing ability of this phenolic Mannich base toward rare earth ions showed that Eu 3+ , Dy 3+ and Gd 3+ induce changes in the absorption spectrum of the Mannich base. Fluorescence spectroscopy showed that the response of the sensing molecule toward Eu 3+ and Dy 3+ 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 −5 M). A phenolic Mannich base derived from 1′-hydroxy-2′-acetonaphthone 1 was synthesised. It demonstrated the ability to act as a fluorescent sensor for Al 3+ , exhibiting a "turn-on" response, and for Cu 2+ , exhibiting a "turn-off" response.