Selective fluorescence sensing of zinc and mercury ions with hydrophilic 1,2,3-triazolyl fluorene probes

The ability to rapidly detect biologically and environmentally significant metal ions such as zinc and mercury is important to study a number of important cellular and environmental processes. Hydrophilic bis(1,2,3-triazolyl)fluorene- based derivatives containing a 1,2,3-triazole-based recognition moiety were synthesized through Click chemistry and characterized by UV-vis absorption, fluorescence emission, and two-photon absorption as new fluorescence sensing probes, selective for Zn²⁺ and Hg²⁺ ions. The UV-vis absorption and fluorescence emission spectra of the complexes exhibited blue-shifted absorption and emission spectra upon chelation to Zn²⁺ and Hg²⁺ ions, resulting in ca. 2-fold enhancement in fluorescence. Fluorometric titration revealed that 1:2 and 1:3 ligand to metal complexes formed with binding constants of 10⁸ and 10¹⁶ for Zn ²⁺ and Hg²⁺, respectively. The two-photon absorption cross sections for the probes and probe-metal ion complexes ranged from 200 to 350 GM at 800 nm. These novel fluorescent compounds may have potential as new metal ion sensors to probe cellular and biological environments.