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Near-IR emissive lanthanoid cryptates have been developed with the lanthanoids Yb, Nd, Er, and Pr by designing a fully deuterated ligand environment that greatly suppresses multiphonon nonradiative deactivation pathways through avoidance of high-energy oscillators and rigidification of the ligand backbone. Strong luminescence is observed in CD(3)CN for all four lanthanoids. Luminescence lifetimes in CD(3)CN are among the highest values for molecular complexes in solution reported so far (Yb, τ(obs) = 79 μs; Nd, τ(obs) = 3.3 μs). For the ytterbium cryptate, the highest luminescence lifetime can be obtained using CD(3)OD (τ(obs) = 91 μs) and even in nondeuterated CH(3)CN the lifetime is still unusually high (τ(obs) = 53 μs). X-ray crystallography and (1)H NMR analysis of the corresponding nondeuterated lutetium cryptate suggest that the inner coordination sphere in solution is completely saturated by the octadentate cryptand and one chloride counterion. All lanthanoid cryptates remarkably show complete stability during reversed-phase HPLC measurements under strongly acidic conditions.
Doffek et al. (Tue,) studied this question.