Sterically crowded phenanthrolinediamides: conformational behavior and photophysics of their complexes with an Eu-Gd-Tb triad.

Three positional isomers of alkyl-aryl-substituted 1,10-phenanthroline-2,9-dicarboxamides (DAPhens) were synthesized and investigated. Using quantum chemical modeling, the difference in the conformational behavior of new DAPhens and their complexes characterized by the presence of alkyl substituents in the aryl fragment of the amide function was demonstrated. The coordination chemistry of the synthesized diamides has been studied in detail using spectroscopic methods and X-ray diffraction analysis. Complex compounds of DAPhens with trinitrates of selected rare-earth elements, including europium, gadolinium and terbium, were synthesized. The photophysical properties of these complex compounds were examined, revealing that the highest quantum yield is achieved for the complex containing symmetric 2,6-dimethylphenyl-DAPhen.