Chiral recognition phenomena probed by steady-state luminescence measurements: Stern-Volmer analysis of chiral discriminatory behavior.

Abstract

The chiral recognition phenomenon observed in enantioselective excited-state energy transfer processes currently requires the use of chiroptical spectroscopic techniques to probe the magnitude and sense of the discriminatory interactions. The use of chiroptical spectroscopic techniques limits the study of chiral recognition to those molecular species with strong absorption or emission dissymmetry factors. This study presents the theoretical and experimental methodology to determine the magnitude of chiral discriminatory interactions with unpolarized, steady-state luminescence measurements. Based on bimolecular luminescence quenching kinetics for a system containing chiral molecules, the Stern-Volmer equation is derived and contains a chiral discriminatory term for a system containing a chiral but racemic luminophore and an enantiomerically resolved quencher species. The utility of this methodology is confirmed by examining the enantioselective excited-state quenching between several Ln(dpa)(3)(3-) complexes (where Ln = Eu(3+), Tb(3+), or Dy(3+) and dpa = pyridine-2,6-dicarboxylate) acting as the energy donor and either racemic or enantiomerically resolved [Co(dach)(3)](3+) (where dach = trans-1R,2R (or 1S,2S)-diaminocyclohexane) acting as the energy acceptor in an aqueous solution. The results of this study confirm the utility of unpolarized, steady-state luminescence measurements as a probe of chiral discriminatory behavior.