Analytical Sciences

New “Off-On” Responsible Fluoroionophores for Alkaline Earth Metal Ions Based on Benzo-15-crown-5 Bearing 9-Phenanthreneacetamide

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

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

The photochemical behaviors of a series of 9-phenanthreneacetamide (PA) derivatives were investigated using UV, fluorescence, and ¹H-NMR spectroscopy in acetonitrile solutions. To apply the electron transfer (ET) action of PA as a detecting moiety of chemosensors, 4′-(9-phenanthreneacetamido)-benzo-15-crown-5 (1) and 3′-methyl-4′-(9-phenanthreneacetamido)-benzo-15-crown-5 (2) were synthesized. After metal ion complex formation, the fluorescence intensity increased with increased concentration of the guest alkaline earth metal ions. The photochemical responses of the fluorescence intensity, as defined by the fluorescence intensity ratio (I_max/I₀) between free and complex of 1 for Ca²⁺, was determined to be 4.76. However, the addition of guest ions in a solution of 2 greatly enhanced the fluorescence intensity of 2. The I_max/I₀ of 2 was 16.6 for Ca²⁺. The efficiency of ET of PA can be tuned by adding an electron-donating group onto a suitable position; fluorescent 2 was able to read out metal ions as an “Off-On” fluorescence signal.

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