Energy Transfer Analysis Of Terpyridyl Europium(III) Complexes With Distinct Crystal Polarity

Lanthanide(III) metals have unique properties which allows them to be used as chiral probes that can help us understand the photophysical properties of ligands complexed to them. Understanding these properties will provide information about the chiral and physiological effects of the ligands in the complex.

 In this study, two chiral terpyridyl (TPY) Eu(III) complexes: Eu(TTA)₃(±TPY) and Eu(BTA)₃(±TPY) (tta = 2-thenoyltrifluoroacetonate and bta = benzoyltrifluoroacetonate); were investigated to characterize the energy transfer from the ligand molecules to the Eu(III) within the two complexes.

Given the difference in crystal polarity of the two chiral TPY Eu(III) complexes, we hypothesis that there will be a difference in the energy transfers within these two complexes.

The diastereoisomers of both Eu(III) complexes were analyzed spectroscopically. For all complexes, steady-state and time-resolved luminescence, and quantum yield measurements indicated inefficient inter-system crossing (ISC) energy transfer but efficient overall energy transfer from the ligand molecules to the Eu(III) metal. Lifetime measurements indicated that one Eu(III)-containing species existed in each sample of our complexes of interest. Circularly polarized luminescence (CPL) measurements indicated while solvated structures of the complexes were similar and that the complex which crystallized in the polar space group had a higher chiroptical activity.

Our results suggest that the complex that crystallizes in the polar space group has more optical activity and energy transfer. Therefore, crystal polarity of lanthanide(III) complexes should be considered when using them as probes for the chirality.