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

A new intramolecular charge transfer (ICT) probe 3 is found to display a highly selective photophysical response in the presence of Zn2+, 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 Zn2+. The binding interaction follows the order Zn2+ > Cd2+ > Mg2+ > Ba2+ > Ca2+ > K+ ≅ Na+ ≅ Li+ and the stability constant for 3 + Zn2+ is over an order of magnitude higher compared to biologically competing Ca2+ and Mg2+.