Dependence of the Photophysical Properties on the Number of 2,2′-Bipyridine Units in a Series of Luminescent Europium and Terbium Cryptates

The luminescence properties of a series of lanthanoid
cryptates
with an increasing number of 2,2′-bipyridine units have been
investigated for the lanthanoids Eu and Tb in aqueous solution. The
trends in important parameters that influence the photophysics in
these complexes have been determined. With increasing bipyridine content,
an increase is observed for the intersystem crossing efficiencies
and the number of inner-sphere water molecules. In contrast, a decrease
is found in the same direction for overall quantum yields, triplet
energies, and sensitization efficiencies.