A new intramolecular charge transfer receptor as a selective ratiometric ‘off–on’ sensor for Zn2+

Abstract A new intramolecular charge transfer (ICT) probe 3 is found to display a highly selective photophysical response in the presence of Zn 2+ , among various biologically significant metal ions examined. The absorption band of 3 is red shifted by 84 nm and the fluorescence intensity increases 13-fold in the presence of Zn 2+ . The binding interaction follows the order Zn 2+  > Cd 2+  > Mg 2+  > Ba 2+  > Ca 2+  > K +  ≅ Na +  ≅ Li + and the stability constant for 3  + Zn 2+ is over an order of magnitude higher compared to biologically competing Ca 2+ and Mg 2+ .