A New Multifunctional Phenanthroline-Derived Probe for Colorimetric Sensing of Fe2+ and Fluorometric Sensing of Zn2+

A new phenanthroline derivative bearing imidazole group, (2-(3,5-di(pyridin-4-yl)phenyl)-1-p-tolyl-1H-imidazo[4,5-f][1,10]phenanthroline) has been devised. The derivative serves as a multifunctional probe, exhibiting a highly sensitive colorimetric response to Fe2+ ion and a selectively ratiometric fluorescent response to Zn2+ ion in a buffer-ethanol solution. The colorless-to-red visual color change upon addition of Fe2+ accompanied by enhanced absorption makes this derivative a suitable naked-eye sensor for Fe2+ ion. Moreover, the derivative displayed a Zn2+-induced red-shift of emission (44 nm), showing a color change from blue to light cyan under a 365-nm UV lamp. Its practical imaging applicability for intracellular Zn2+ was confirmed in HeLa cells using a confocal microscope. The improved emission properties and cell imaging capability would provide a new approach to fluorescence sensation for Zn2+.