CPL Intensity Calculations, Selection Rules, Luminescence Selectivity, and Spectra-Structure Relationship

2 CPL Intensity Calculations, Selection Rules, Luminescence Selectivity, and Spectra—Structure Relationship 

The emphasis in much of the CPL-based work developed over the past decade is a result of the unusual spectral characteristics of the luminescent chiral Ln(lll) complexes (see Chapter 1) and the technical advantages resulting from the use of CPL. One ean expect the measurement of larger values when the transitions involved are inherently weak. This can be seen from the form of Equation 3.12 where one may expect a large value when the transition considered is electric dipole forbidden, but magnetic dipole allowed. Since the magnetic dipole transition moments are typically much smaller than the electric dipole terms, the denominator in Equation 3.12 will be dominated by the first term, p. Transitions 

This example shows that one needs to be careful on how to interpret CPL results with respect to the distribution of complex species present in solution. It is essential to know what the sample solution contains to avoid misinterpretation, since the CPL and total luminescence intensity from solutions of Ln(III) complexes with a mixture of ligands (i.e. some of which may be chiral or not, or in situations in which one chiral ligand may form multiple solution species) may come from different species [38]. For instance, such a solution of Tb(ni) with dipicolinic acid (DPA) and L-malic acid showed that the total luminescence 

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