Binuclear Lanthanide Complexes as Magnetic Resonance and Optical Imaging Probes for Redox Sensing.

We report a family of lanthanide(III) complexes that act as redox probes via both magnetic resonance (MR) and luminescence outputs. The ligands are functionalized with nitro, azobenzene and azide groups which are reduced to a common aniline product, and each responds to both chemical and biocatalytic reductive conditions at different cathodic onset potentials. By judicious choice of complexed Ln(III), the probes can be optimized either for use in MR imaging (Ln = Gd), or as highly efficient turn-on luminescence probes (Ln = Tb). The Tb(III) analogues are essentially nonemissive, until reductive generation of the aniline affords a complex which when excited by visible light (488 nm) emits green light with a quantum yield of 45% and millisecond long luminescent lifetimes (ms). The tunable redox response and imaging modalities of these versatile complexes have the potential to open up new approaches to redox sensing, such as the imaging of hypoxic environments in biology.