Synthesis, Stability and Sensitised Lanthanide Luminescence of Heterobimetallic d/f Terpyridine Complexes

The synthesis, solution behavior and photophysical properties of several heteronuclear bimetallic d/f complexes that utilise a RuII bis-terpyridine moiety as the sensitiser for EuIII, NdIII and YbIII luminescence are reported and compared to a GdIII analogue. The former compounds display sensitised emission in the visible and near-infrared (NIR) regions depending on the choice of the LnIII cation. We illustrate that sensitised lanthanide emission can operate by two distinctly different pathways that involve either the triplet ligand-centred (3LC) excited state of the organic ligand or the triplet metal-to-ligand charge transfer (3MLCT) excited state of the RuII complex. Owing to the electronic structure of this antenna and the higher density of metal-centred accepting states, a higher sensitization efficiency with NdIII was observed than with YbIII and EuIII. Lastly, we have observed unusual sensitised emission from the upper (4F5/2, 2H9/2) excited state of NdIII at approximately 800 nm, which we report here for the first time from a molecular species in solution.