Sensitised lanthanide luminescence using a RuIIpolypyridyl functionalised dipicolinic acid chelate

A visible light absorbing [RuII(tpy)2]2+-type chromophore appended with a dipicolinic acid LnIIIchelator has been prepared and complexed with several differing lanthanide cations to form the corresponding heterobimetallic d-f assemblies. The subseqent solution speciation analysed by1H NMR spectroscopy revealed an unexpected decrease in the LnIIIchelate complex stability, in particular for the 1 : 3 complex, when compared to the parent dipicolinic acid. As a result, the desired Ln(ML)3complexes could not be isolated, and the 1 : 1 LnIII-ML complexes were instead characterised and investigated using steady state absorption and emission spectroscopy. Sensitised NIR emission from the YbIII, NdIIIand ErIIIcomplexes was observed upon1MLCT excitation of the RuIIbased metalloligand in the visible region atca.485 nm. Investigations using transient absorption spectroscopy revealed essentially quantitative intersystem crossing to form the3MLCT excited state, as expected, which then acts as the energy donor for the metalloligand based antennae effect, facilitating sensitisation efficiencies of 4.8, 17.0 and 37.4% respectively for the YbIII, ErIIIand NdIIIcations.</p