Dynamic chiral quenching of europium and terbium excited states

Abstract

The nature of dynamic quenching of the europium or terbum excited states in Δ and Λ stereoisomeric cationic complexes by S and R Trolox has been studied by emission and CPL spectroscopy and DFT computations. Non-linear Stern-Volmer quenching kinetics were observed and the stereoselective behaviour was interpreted in terms of an exciplex model, where the binding constant for exciplex formation, Kex , and the rate constant for exciplex decay, k3 , determine overall quenching efficiency. Dynamic quenching was most efficient with R Trolox for the Δ Eu and Tb complexes in three systems. Ground state DFT calculations revealed that the Δ complex with S Trolox was 10 kJ mol-1 lower in energy than with R Trolox, yet was quenched less efficiently, suggesting that the origins of the observed chiral quenching behaviour are not associated with the relative stabilities of each exciplex, but with their relative rates of decay.