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 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 rate by a factor of 3 compared to GdDOTA. In addition, Nd1 and Yb1 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. Lanthanide DO3A-Tropone Complexes: Efficient Dual MR/NIR Imaging Probes in Aqueous Medium. Available from: https://www.researchgate.net/publication/319274985_Lanthanide_DO3A-Tropone_Complexes_Efficient_Dual_MRNIR_Imaging_Probes_in_Aqueous_Medium [accessed Nov 13 2017].