Excitation Energy-Transfer Processes in the Sensitization Luminescence of Europium in a Highly Luminescent Complex.

The excitation energy transfer (EET) pathways in the sensitization luminescence of Eu and the excitation energy migration between the different ligands in [Eu(fod)dpbt] [where fod=6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione and dpbt=2-(,-diethylanilin-4-yl)-4,6-(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine], exhibiting well-separated fluorescence excitation and phosphorescence bands of the different ligands, were investigated by using time-resolved luminescence spectroscopy for the first time. The data clearly revealed that upon the excitation of dpbt, the sensitization luminescence of Eu in [Eu(fod)dpbt] was dominated by the singlet EET pathway, whereas the triplet EET pathway involving T(dpbt) was inefficient. The energy migration from T(dpbt) to T(fod) in [Eu(fod)dpbt] was not observed. Moreover, upon the excitation of fod, a singlet EET pathway for the sensitization of Eu luminescence, including the energy migration from S(fod) to S(dpbt) was revealed, in addition to the triplet EET pathway involving T(fod). Under the excitation of dpbt at 410 nm, [Eu(fod)dpbt] exhibited an absolute quantum yield for Eu luminescence of 0.59 at 298 K. This work provides a solid and elegant example for the concept that singlet EET pathway could dominate the sensitization luminescence of Eu in some complexes.