ANALYSIS OF ENANTIOSELECTIVE QUENCHING OF TB(2,6-PYRIDINEDICARBOXYLATE)3(3-) LUMINESCENCE BY RESOLVED RU(1,10-PHENANTHROLINE)3(2+) IN METHANOL AND IN WATER

Circularly polarized luminescence is observed from racemic solutions of Tb(2,6-pyridinedicarboxylate)3(3-) when small amounts of resolved Ru(1,10-phenanthroline)3(2+) are added. This phenomenon has been attributed to enantioselective quenching of the terbium complex by the ruthenium species, resulting in a nonracemic excited-state population. In this work, a simple kinetic scheme for this quenching process is presented, and it is demonstrated that the individual diastereomeric rate constants may be determined directly through numerical fitting of the biexponential decay of the total luminescence intensity. This is shown to give essentially the same results as numerical fitting of the time decay of the luminescence dissymmetry factor when data from both of these measurement techniques are available. It is also demonstrated that the enantioselectivity in the chiral quenching is solvent dependent. In aqueous solutions, for example, addition of DELTA-(-)-Ru(phen)3(2+) results in an excess of DELTA-Tb(DPA)3(3-), i.e., the DELTA enantiomer is quenched more efficiently, whereas in methanol the opposite enantiomer is in excess.