Lanthanide DO3A-tropone complexes: efficient dual MR/NIR imaging probes in aqueous medium.

In this work, we describe a novel DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) based ligand with a chromophoric tropone coordinating sidearm (). Ln complexes of have one inner sphere water molecule. The r relaxivity of Gd is similar to that of the commercial Gd-based MRI agents. The neutral O-donor atom of the tropone moiety slows down the water exchange rate by a factor of 3 compared to GdDOTA. In addition, Nd and Yb complexes exhibit significant NIR emission in aqueous solutions indicating that the tropone unit is an efficient sensitizer for these Ln-ions. Therefore, this new ligand is a promising platform for the design of Ln based dual MR/optical imaging probes.