Synthesis, photophysical and assembly studies of novel luminescent lanthanide(III) complexes of 1,2,3-triazolyl-pyridine-2,6-dicarboxamide-based ligands

The well-known lanthanide-binding motif, 2,6-pyridinedicarboxamide, has been functionalised with peripheral substituents using copper-catalysed azide alkyne coupling (CuAAC) to develop new symmetrical ‘clicked’ N₂,N₆-bis((1-(X)-1H-1,2,3,-triazol-4-yl)methyl)pyridine- 2,6-dicarboxamide (where X = ethyl (1) benzyl (2) and 2-naphthyl (3)). These ligands have been successfully coordinated with trivalent lanthanide ions (europium, terbium, and lanthanum) forming [Ln(L)₃](CF₃SO₃)₃ complexes. The ligands act as effective antennae for Eu³⁺ and Tb³⁺ complexes, which exhibit the characteristic sensitised emission profiles. The ability of 1–3 to assemble into 1:3 M:L systems in solution was investigated using UV-Vis, fluorescence, and NMR. Finally, density functional calculations of the ground state La³⁺ complexes have been carried out and show similar geometry and coordination parameters to those with available crystallographic data. The facile and modular synthesis of these ‘clicked’ PDC-based ligands makes these compounds excellent candidates for luminescent supramolecular materials development.