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 (ligand 1 ). Ln 3+ complexes of 1 have one inner‐sphere water molecule. The r 1 relaxivity of Gd 1 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 by a factor of 3 compared to that for GdDOTA. In addition, complexes Nd 1 and Yb 1 exhibit significant NIR emission in aqueous solutions, which indicates that the tropone unit is an efficient sensitizer for these Ln 3+ ions. Therefore, this new ligand is a promising platform for the design of Ln 3+ ‐based dual MR/optical imaging probes.