A Promising Change in the Selection of the Circular Polarization Excitation Used in the Measurement of Eu(III)Circularly Polarized Luminescence

摘要

A judicious change in the selected transition used for circular polarization excitation will overcome the low oscillator strength limitation of the currently allowed magnetic-dipole ~5D_1-~7F_2(Eu(III))transition chosen for circularly polarized luminescence(CPL)measurement.The proposed allowed magnetic-dipole ~5D_1<-~7F_0(Eu(III))transition will facilitate the detection of CPL from the Eu(III)systems of interest.CPL on the acetonitrile solution of the chiral tris complex of Eu(III)with(R,R)-N,N'-bis(l-phenylethyl)-2,6-pyridinedi-carboxamide([Eu((R,R)-1)3]~(3+)),recently suggested as an effective and reliable CPL calibrating agent,confirms the feasibility of the proposed experimental procedure.A comparable CPL activity exhibited by the acetonitrile solution of[Eu((R,R)-1)3]~(3+)following direct excitation in the spectral range of the ~5D_1<-~7F_0 transition and upon indirect excitation through the ligand absorption bands(lambda_(exc)=308 nm)was observed.This confirms that the recommended magnetic-dipole allowed absorption transition,~5D_1<-~7F_0,is the transition to be considered in the measurement of CPL.This work provides critical direction for the continued instrumental improvements that can be done for developing CPL into a biomolecular structural probe.