Metal-coordination-mediated sequential chelation-enhanced fluorescence (CHEF) and fluorescence resonance energy transfer (FRET) in a heteroditopic ligand system

Sequential fluorescence enhancement and fluorescence resonance energy transfer over a zinc ion gradient have been engineered in a two-fluorophore heteroditopic ligand platform. This is the first report that the strategies of metal-coordination modulated photoinduced electron transfer (PET), internal charge transfer (ICT), and fluorescence resonance energy transfer (FRET) are integrated in one synthetic fluoroionophore. Comparing to the previously reported single-fluorophore heteroditopic ligands (L. Zhang, R. J. Clark and L. Zhu, Chem. Eur. J. 2008, 14, 2894-2903), the resolution of two emission channels is greatly enhanced to almost 100 nm. This two-fluorophore heteroditopic platform lends promise to creating dual-emission fluorescent indicators where low-and high-target concentration regimes could be analyzed using independent emission filter sets.