Rigid, Perdeuterated Lanthanoid Cryptates: Extraordinarily Bright Near-IR Luminophores.

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 CD3CN for all four lanthanoids. Luminescence
lifetimes in CD3CN are among the highest values for molecular
complexes in solution reported so far (Yb, τobs =
79 μs; Nd, τobs = 3.3 μs). For the ytterbium
cryptate, the highest luminescence lifetime can be obtained using
CD3OD (τobs = 91 μs) and even in
nondeuterated CH3CN the lifetime is still unusually high
(τobs = 53 μs). X-ray crystallography and 1H 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.