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 ( 1 ). Ln3+ complexes of 1 have one inner sphere water molecule. The r1 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 rate by a factor of 3 compared to GdDOTA. In addition, Nd 1 and Yb 1 complexes exhibit significant NIR emission in aqueous solutions indicating 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.