Asymmetric fluorescence quenching of dual-emissive porphyrin-containing conjugated polyelectrolytes for naked-eye mercury ion detection

A series of cationic porphyrin-containing conjugated polyfluoreneethynylenes (PFEs) are synthesized for mercury(II) detection. The incorporation of porphyrin into the PFE backbone offers dual emissive polyelectrolytes with both blue and red emission bands resulting from incomplete intramolecular energy transfer from the fluoreneethynylene segments to the porphyrin units. In the presence of mercury(II), both blue emission from the fluoreneethynylene segments and red emission from the porphyrin units are quenched, and the quenching in red emission is significantly larger than that in blue emission. In the presence of other metal ions, for example, Zn ²⁺, Cu²⁺, Cd²⁺, Pd²⁺, Co ²⁺, and Ni²⁺, there is almost no change observed in red porphyrin emission, while the quenching in blue fluoreneethynylene emission is observed. The asymmetric quenching of the blue and red emission bands in the presence of various metal ions leads to real-time mercury(II) detection. Using a standard fluorometer, the fluorescence quenching of porphyrin for the best polymer has shown a linear response to mercury(II) in the concentration range of 0-100 μM, with a detection limit of 0.1 μM. In addition, the fluorescent color change of the polymer solution allows naked-eye detection of mercury(II) with a detection limit of 10 μM.