Anomalous Reversal of C-H and C-D Quenching Efficiencies in Luminescent Praseodymium Cryptates

A series of selectively deuterated praseodymium cryptates has been synthesized. Their luminescence lifetimes in solution range from 150 to 595 ns for the D-1(2) -> F-3(4) transition. Global fitting of the nonradiative deactivation rate differences of the isotopologic C-(H/D) oscillators revealed that aromatic C-D overtones anomalously quench the luminescence more than C-H vibrations. This is explained by the dominance of Franck-Condon overlap factors that greatly favor C-D oscillators, which are in almost ideal resonance with the relevant energy gap D-1(2)-(1)G(4) of praseodymium.