Novel neutral lanthanide complexes of 5-aryl-2,2′-bipyridine-6′-carboxylic acids with improved photophysical properties

By means of “1,2,4-triazine” strategy new 2,2′-bipyridine-type lanthanide ligands, i.e. 5-aryl-2,2′-bipyridine-6′-carboxylic acids and its cycloalkane-annulated derivatives, i.e. 6-(4-aryl-6,7-dihydro-5H-cyclopenta[c]pyridin-1-yl)picolinic acids, have been synthesized, and their luminescent neutral lanthanide complexes have been prepared. Due to the presence of an annulated cyclopentene fragment the last ligand lanthanide complexes exhibited high solubility in non-polar solvents. In comparison with early published chelates the herein reported complexes exhibit improved photophysical properties in non-polar solvents namely more pronounced bathochromic shift in absorption spectra and higher europium luminescence quantum yields. The structures of two europium complexes have been confirmed based on X-ray diffraction analysis.