A bipyridine-based “naked-eye” fluorimetric Cu2+ chemosensor

A series of six 2,2′-bipyridine-3,3′-diols with different substituents have been synthesized and characterized. The designed ligands show fluorescence in the visible part of the spectra, but only the luminescence of the less sterically hindered molecules is quenched in the presence of Cu²⁺ ions. Selectivity and sensitivity of the chemosensors have been tested by absorption and luminescence spectroscopy in aqueous solutions, with a dynamic working range of 0.7-30 μM and a limit of detection of 0.04 ppm (mg L^-1).