Iodinated Metallacrowns: Toward Combined Bimodal Near-Infrared and X-ray Contrast Imaging Agents

Multimodal probes capable of combining imaging modalities within a single molecule are in high demand today as they can provide information at both molecular and anatomical levels. Herein, a study was conducted on a series of gallium(III)/lanthanide(III) bis(12-MC-4) metallacrowns (MCs) with the general composition {Ln[12-MCGa (III) N(shi) -4]}2 (iph)4 (Ln-Ix , x=0, 4, 8, 12), where shi and iph are salicylhydroximate and isophthalate ligands, respectively, or their iodinated derivatives. For Yb-Ix , the attenuation in X-ray computed tomography (XCT) imaging and near-infrared (NIR) luminescence properties can be finely tuned by controlled structural modifications based on iodo groups. Solutions of Yb-Ix appear to be 22-40 times more efficient as XCT agents in comparison to the commercially available iobitridol, while providing an intense emission signal in the NIR range with total quantum yields up to 8.6 %, which are among the highest values reported so far. Therefore, these molecules are promising potential bimodal agents for combined NIR luminescence and XCT imaging.