Photophysical and Chiroptical Properties of the Enantiomers of N,N' ‐Bis(1‐phenylpropyl)‐2,6‐pyridinecarboxamide and their Chiral 9‐Coordinate Ln 3+ Complexes

The R,R and S,S enantiomers of N,N' ‐bis(1‐phenylpropyl)‐2,6‐pyridinedicarboxamide, L(Et) , react with Ln 3+ ions (Ln = La, Eu, Gd, and Tb) to give stable [Ln(( R,R )‐ and ( S,S )‐ L(Et )) 3 ] 3+ in anhydrous acetonitrile solution, as evidenced by various spectroscopic measurements, including NMR and luminescence titrations. In addition to the characteristic Eu 3+ and Tb 3+ luminescence bands, the steady‐state and time‐resolved luminescence spectra of the aforementioned complexes show the residual ligand‐centered emission of the 1 ππ* to 3 ππ* states, indicating an incomplete intersystem crossing (ISC) transfer from the 1 ππ* to 3 ππ* and ligand‐to‐Ln 3+ energy transfer, respectively. The high circularly polarized luminescence (CPL) activity of [Eu( L(Et) ) 3 ] 3+ confirms that using a single enantiomer of L(Et) induces the preferential formation of one chiral [Eu( L(Et) ) 3 ] 3+ complex, consistent with the [Eu L 3 ] 3+ complexes formed with other ligands derived from a 2,6‐pyridine dicarboxamide moiety. Furthermore, the CPL sign patterns of complexes with ( R,R ) or ( S,S ) enantiomer of L(Et) are consistent with the CPL sign pattern of related [Ln L 3 ] 3+ complexes with the ( R,R ) or ( S,S ) enantiomer of the respective ligands in this family.