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). Ln3+ complexes of 1 have one inner‐sphere water molecule. The r1 relaxivity of Gd1 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 Nd1 and Yb1 exhibit significant NIR emission in aqueous solutions, which indicates that the tropone unit is an efficient sensitizer for these Ln3+ ions. Therefore, this new ligand is a promising platform for the design of Ln3+‐based dual MR/optical imaging probes. A DOTA derivative with a tropone coordinating sidearm forms monohydrated lanthanide complexes. The Gd3+‐chelate has the expected relaxivity while the Nd3+ and Yb3+ complexes exhibit bright NIR luminescence despite the quenching effect of the inner‐sphere water molecule.