Photophysical and Chiroptical Properties of the Enantiomers of N,N'‐Bis(1‐phenylpropyl)‐2,6‐pyridinecarboxamide and their Chiral 9‐Coordinate Ln³⁺ Complexes

Abstract

The R,R and S,S enantiomers of N,N'‐bis(1‐phenylpropyl)‐2,6‐pyridinedicarboxamide, L(Et), react with Ln3+ 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 Eu3+ and Tb3+ luminescence bands, the steady‐state and time‐resolved luminescence spectra of the aforementioned complexes show the residual ligand‐centered emission of the 1ππ* to 3ππ* states, indicating an incomplete intersystem crossing (ISC) transfer from the 1ππ* to 3ππ* and ligand‐to‐Ln3+ 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 [EuL3]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 [LnL3]3+ complexes with the (R,R) or (S,S) enantiomer of the respective ligands in this family.

Sorting Phenomena and Chirality Transfer in Fluoride-Bridged Macrocyclic Rare Earth Complexes

“…However, the observation of the CPL activity for the Eu(III)-containing compounds tends to favor an efficient Tb(III) back-transfer phenomenon. 87 …”

“…However, the observation of the CPL activity for the Eu(III)-containing compounds tends to favor an efficient Tb(III) back-transfer phenomenon. 86 Crystal Structures of Fluoride-Bridged Homodinuclear Ln (III) 5, Figures S1 and S2) indicates two parallel macrocyclic units linked by two bridging fluoride anions. The crystal of this compound contains the cationic complex [Lu 2 (L1 R ) 2 (μ 2 -F) 2 (NO 3 ) 2 ] 2+ , free nitrate counterions, and solvent molecules.…”

“…The intensity was too weak, suggesting that there is most likely an effective back-transfer from the Tb­(III) to the ligand and/or an inefficient intersystem crossing between the singlet and triplet states of the ligand taking place for the Tb­(III)-containing complexes. However, the observation of the CPL activity for the Eu­(III)-containing compounds tends to favor an efficient Tb­(III) back-transfer phenomenon …”

Ancillary ligand modulated stereoselective self-assembly of triple-stranded Eu(iii) helicate featuring circularly polarized luminescence

“… 5 Lanthanide helicates are regarded as the favorable candidates of CPL materials in view of their supramolecular helical chirality and the characteristic electron transition from Ln 3+ ions. 6 The partial magnetic dipole character endowed the Ln 3+ ions with a higher luminescence dissymmetry factor ( g lum ), 7 typically in the range of 10 −2 –0.5, 8 which is obviously larger than those of pure organic luminophores ( g lum = 10 −5 –10 −3 ). 9 To date, the highest g lum value for CPL materials in solution was recorded to be 1.38 from a Eu 3+ complex, Cs[Eu((+)-hfbc) 4 ].…”

Sorting Phenomena and Chirality Transfer in Fluoride-Bridged Macrocyclic Rare Earth Complexes

“…IR spectra were recorded with Bruker Vertex 70 FTIR instrument, using KBr pellets.Circularly polarized luminescence (CPL) and total luminescence spectra were recorded on an instrumentation described previously. 1 In short, the instrumentation is equipped with a 1000 W xenon arc lamp from a Spex FluoroLog-2 spectrofluorometer, with excitation and emission monochromators of dispersions 4 nm/mm (SPEX, 1681B). The optical detection system consisted of a focusing lens long-pass filter and 0.22 m monochromator.…”