Analytical Sciences

The “Off-On” Fluorescence Detection of Alkaline Earth Metal Ions by Using 1-Naphthylacetanilide Derivatives: New Cation Sensors Based on Oligo-ethylene Oxides Connecting 1-Naphthylacetanilide at Its Terminals

Tatsuya MOROZUMI,* Hiroya HAMA,** and Hiroshi NAKAMURA*

*Section of Materials Science, Research Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan
**Division of Environmental Material Science, Graduate School of Environmental Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan

New fluorescent ionophores containing the 1-naphthylacetanilide moiety based on oligo-ethylene oxide (1₄ and 1₅) have been synthesized, and their photochemical behaviors have been studied. In the absence of a metal ion, the 1-naphthylacetanilide moiety showed a weak fluorescence emission (fluorescence “off state”). However, complexation with Ca²⁺ induced a large enhancement effect on the fluorescence intensity of 1₄ and 1₅ from the naphthalene ring (fluorescence “on” state). This behavior can be explained in terms of a similar twisted intramolecular charge-transfer relaxation mechanism. Such “off-on” fluorescence responses of 1₄ and 1₅ provide the digital detection of alkaline earth metal ions.

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