Survey of CPL Applications

In order to detect a CPL signal, the emitting species must be chiral. The key point of introducing chirality into luminescent Ln(III) complexes is to develop strongly luminescent probes that also possess chiral properties with the goal of improving the selectivity toward biological systems. One of the enantiomers/diastereoisomers of the chiral Ln(III) complex 

1 CPLfrom Racemic Mixtures following Circularly Polarised Excitation 

The use of achiral ligands usually leads to the formation of Ln(III) complexes existing as racemic mixtures of complexes with A and A hehcity in solution (Fig. 3.6). It is worth noting that there is only one example for which CPL has been conducted on a chiral luminescent Ln(ni) complex containing achiral ligands that has been resolved and smdied in solution [AA-(-)EuCr(L )3 +] [89]. 

One unique aspect of the CPL spectroscopy is that it can identify whether a Ln(Ill) complex solution contains a mixture of diastereomeric/enantiomeric species or whether this complex solution is a racemic mixture. If only one emitting species contributes to the luminescence observed in the sample, then the CPL results should be independent of excitation polarisation. Variation of the excitation polarisation from left to right circular polarisation will produce an oppositely signed CPL result of equal magnitude for a racemic 

In addition to verify if a Ln(III) complex with achiral ligands exists as a racemic mixture in solution, the CPL spectroscopy is also often used as a probe of specific molecular chirality. It was shown that the luminescent fm-terdentate Ln(lII) complexes of ligands derived from DPA are good candidates for such studies. Of special importance is that the modular nature of the DPA backbone allows for easy synthesis of derivatives with tunable photophysical and/or chiroptical properties [94]. This is the reason why they are often used for chirality 

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