Circularly polarized luminescence spectra

Fig. 11.4. Part of the circularly polarized luminescence spectrum of the Tb3+-porcine trypsin complex showing...

The Pfeiffer effect, the outer-sphere interaction of a chiral substrate with a rapidly interconverting racemic solution of a chiral lanthanide complex, can be investigated by measurement of the luminescence dissymmetry factor (the ratio of circularly polarized luminescence to total luminescence) for Eu or Tb " complexes. Thus the racemic D chiral complexes [M(dpa)3], where M = Eu or Tb, interact in an outer-sphere manner with the following optically active spiecies cationic chiral transition metal complexes, ascorbic acid, aminocarboxylates, tartrates, amines and phenols. Association constants can be obtained from limiting values of the dissymmetry factors. In some cases, inner-sphere complexation can be demonstrated, as judged by changes in the general nature of the circularly polarized luminescence spectrum and pH irreversibility of the complexation. 

The J sublevels of rare earths are split by ligand fields of low symmetry. These splittings may be observed in circularly polarized luminescence (CPL) but not in the fluorescence spectrum. Hence CPL spectra provide information on the rare earth ion and thus throw light on the binding site. The emission and CPL spectra of Tb3+ bound to transferrin and cobalbumin were found to be similar leading to the conclusion that the structure and... 

Fluorescence-detected circular dichroism (FDCD) is a chiroptical technique in which the spectrum is obtained by measuring the difference in total luminescence obtained after the sample is excited by left- and right-circularly polarized light. For the FDCD spectrum of a given molecular species to match its CD spectrum, the luminescence excitation spectrum must be identical to the absorption spectrum. 

Figure 5 CPL spectrum (upper curve) and total luminescence (lower curve) for an aqueous solution of Eu(DPA) " using circularly polarized 472.8 nm excitation.

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