Radiative Lifetime, Non-Radiative Relaxation, and Sensitization Efficiency in Luminescent Europium and Neodymium Cryptates - The Roles of 2,2'-Bipyridine-N,N'-dioxide and Deuteration.

Five luminescent tris(bipyridine)-based cryptates with the lanthanoids Eu and Nd have been prepared with a systematic increase in the number of 2,2'-bipyridine-N,N'-dioxide units and with different deuteration levels in the complexing cryptands for the europium species. Careful analysis of the radiative lifetime τrad in these systems reveals that an increase in N-oxide units around the metal centers uniformly lowers τrad by about 30-40 %. The potential involvement of nephelauxetic effects is discussed. Exchange of 30 C-D for C-H oscillators around the europium centers does not affect the radiative lifetimes but decreases non-radiative deactivation and increases the overall luminescence quantum yield in D2 O by 45 %.

Unexpected discovery of calcium cryptates with exceptional stability.

A 2,2'-bipyridine-N,N'-dioxide-based cryptand has been found to exhibit exceptional apparent complex stability for Ca2+ and unusually shows very high selectivity for Ca2+ over trivalent lanthanoid cations. The calcium cryptate is kinetically inert to an extent that it even withstands competition experiments with a 77-fold excess of free DOTA ligand, which is currently the chelator with the highest formation constant for calcium.