Sensitised lanthanide luminescence using a RuII polypyridyl functionalised dipicolinic acid chelate

A visible light absorbing [Ru-II(tpy)(2)](2+)-type chromophore appended with a dipicolinic acid Ln(III) chelator has been prepared and complexed with several differing lanthanide cations to form the corresponding heterobimetallic d-f assemblies. The subseqent solution speciation analysed by H-1 NMR spectroscopy revealed an unexpected decrease in the Ln(III) chelate complex stability, in particular for the 1 : 3 complex, when compared to the parent dipicolinic acid. As a result, the desired Ln(ML)(3) complexes could not be isolated, and the 1 : 1 Ln(III)-ML complexes were instead characterised and investigated using steady state absorption and emission spectroscopy. Sensitised NIR emission from the Yb-III, Nd-III and Er-III complexes was observed upon (MLCT)-M-1 excitation of the Ru-II based metalloligand in the visible region at ca. 485 nm. Investigations using transient absorption spectroscopy revealed essentially quantitative intersystem crossing to form the (MLCT)-M-3 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 Yb-III, Er-III and Nd-III cations.

Automated summary

A visible light-absorbing chromophore appended with a dipicolinic acid Ln(III) chelator was prepared and complexed with different lanthanide cations to form d-f assemblies. Unexpected decrease in Ln(III) chelate complex stability was observed, leading to the formation of 1:1 Ln(III)-ML complexes instead of desired Ln(ML)(3) complexes. Sensitised NIR emission from Yb-III, Nd-III, and Er-III complexes was observed upon excitation of the Ru-II based metalloligand in the visible region.