A pH-responsive, luminescent, dimetallic Eu(III)-containing complex has been synthesized and exhibits a unique mechanism of response. The luminescence-decay rate of the complex is slow, due to a lack of water molecules coordinated to the Eu(III) ions. However, the luminescence-decay rate decreases with increasing pH over a biologically relevant range of 4 to 8. Physical characterization and computational analysis suggest that the pH response is due to protonation of a bridging alkoxide at lower pH values. Modulation of the luminescence-decay rate is independent from the concentration of Eu(III), which we expect to be useful in the non-invasive imaging of in vivo pH.

Molecules containing multiple lanthanide ions have unique potential in applications for medical imaging including the areas of magnetic resonance imaging (MRI) and fluoresence imaging. The study of multilanthanide complexes as contrast agents for MRI and as biologically responsive fluorescent probes has resulted in an improved understanding of the structural characteristics that govern the behavior of these complexes. This review will survey the last five years of progress in multinuclear lanthanide complexes with a specific focus on the structural parameters that impact potential medical imaging applications. The patents cited in this review are from the last five years and describe contrast agents that contain multiple lanthanide ions.

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