Estimating the Donor-Acceptor Distance To Tune the Emission Efficiency of Luminescent Lanthanide Compounds.

The influence of the donor-acceptor distance RL on the photophysical properties, including the emission quantum yield, of two europium complexes with the same coordination number, and thus similar microsymmetries, was investigated by spectroscopic and computational methods. K3[Eu(dipicCbz)3] was synthesized using the new ligand dipicCbz and its photophysical properties compared to Cs3[Eu(dipic)3]. We found that a 50% increase in RL from 4.1 to 6.5 Å results in a substantial decrease in the emission efficiency from 24 to 1.8%.