Lanthanoid Luminophores with Linear, Bipyridine-Based Antenna Ligands

A new, linear octadentate chelator, “en-pypa,” based on 2,2′-bipyridine-6-carboxylic acid, has been developed. This ligand can bind trivalent lanthanoids (e.g., Sm, Eu, Tb, Dy, Tm, Yb, and Lu) very rapidly and yields well-defined complexes that exhibit relatively strong luminescence in aqueous solution. This study reports the synthesis, as well as the structural and photophysical characterization. In addition, nonradiative deactivation of near-infrared luminescence by the ligand N–H oscillators is addressed by comparison of the luminescence from the Yb complexes of en-pypa and its methylated analogue.