Siderophore inspired tetra- and octadentate antenna ligands for luminescent Eu(III) and Tb(III) complexes

Following the success of the siderophore-inspired 1,2-hydroxypyridonate (HOPO) and 2-hydroxisophthalamide (IAM) chromophores in Eu(III) and Tb(III) luminescence, we designed three new ligands bearing both chromophores. Syntheses of the octadentate ligands 3,4,3-LI-IAM-1,2-HOPO and 3,4,3-LI-1,2-HOPO-IAM, where the chromophores are attached to different positions in the (LI=linear) spermine backbone, are reported in addition to a tetradentate ligand based on 1,5-diaminopentane. The Gd(III) complexes were prepared and revealed localized triplet states typical for the IAM and HOPO chromophores. Photophysical characterization of the Eu(III) and Tb(III) complexes revealed that the chromophores need to reside at a primary amine of the spermine backbone to be efficient in lanthanide excitation. These systems help us to understand the antenna effect in siderophore inspired chromophores and could be potential targets for sensing and biological imaging applications. Three antenna ligands bearing 1,2-hydroxypyridonate (HOPO) and 2-hydroxisophthalamide (IAM) chromophores are reported. Photophysical characterization of the Gd(III), Eu(III) and Tb(III) complexes revealed localized triplet states for the chromophores and that they need to reside on a primary amine of the spermine backbone to be efficient in lanthanide excitation. [Display omitted] •2-Hydroxisophthalamide (IAM) and 1,2-hydroxypyridonate (HOPO) mixed ligands are prepared•Photophysical properties of Tb and Eu complexes are reported.•When bound to a primary amine the above chromophores are better in sensitizing Tb and Eu.