Structural and Photophysical Properties of Visible- and Near-IR-Emitting Tris Lanthanide(III) Complexes Formed with the Enantiomers of N,N′-Bis(1-phenylethyl)-2,6-pyridinedicarboxamide

Abstract

The enantiomers of N,N’–bis(1–phenylethyl)–2,6–pyridinedicarboxamide (L), namely (R,R)–1, and (S,S)–1, react with Ln(III) ions to give stable [LnL3]3+ complexes in anhydrous acetonitrile solution and in the solid state, as evidenced by ES–MS, NMR and luminescence titrations, and their X–ray crystal structures, respectively. All [LnL3]3+ complexes (Ln(III) = Eu, Gd, Tb, Yb, and L = (R,R)–1, and (S,S)–1)) are isostructural and crystallize in the cubic space group I23. Although the small quantum yields of the Ln(III)–centered luminescence clearly point to the poor efficiency of the luminescence sensitization by the ligand and the intersystem crossing (ISC) and ligand–to–metal energy transfers, the ligand triplet–excited–state energy seems relatively well suited to sensitize many Ln(III) ion’s emission, for instance, in the VIS (Eu, Tb), NIR (Nd, Yb), or in both regions (Pr, Sm, Dy, Er, Tm).

Probing the Effects of Ligand Isomerism in Chiral Luminescent Lanthanide Supramolecular Self‐Assemblies: A Europium “Trinity Sliotar” Study

“…This is supported by the fact that h sens in both solvents is five times higher for the 1-naphthyl derivatives compared to the 2-naphthyl ones. The F tot values obtained here are also significantly higher than the values obtained by either Piguet or Muller, [11,12] indicating the major role played by the naphthalene groups in shielding the Eu III ions. The use of both circular dichroism (CD) and circularly polarised luminescence (CPL) spectroscopy to analyse the ligands and their Eu III complexes in CH 3 OH further confirmed their chiral nature (Figure 4 and the Supporting Information).…”

“…The analyses suggested a coordination number (CN) of 9 for Eu III as per previous similar systems, [10][11][12] which was confirmed by single-crystal X-ray diffraction analysis.…”

“…[11,12,16] The luminescence efficiency of all the complexes was evaluated by determining their quantum yields (F tot , %) in both CH 3 CN and CH 3 OH solutions using Eu III -trisdipicolinate as a standard (see the Supporting Information and Table 2). These measurements further highlighted the differences in the photophysics of the two systems as the…”

Lanthanide complexes as chiral probes exploiting circularly polarized luminescence

“…64,65 This is illustrated in the case of the tris chelate lanthanide complexes derived using the tridentate ligand L 4 . 66,67 As is apparent from Figure 1.13, this ligand is closely related to DPA in terms of its core structure and it is therefore not surprising that the ligands have been found to arrange around the lanthanide centre in a three bladed 'propeller-like' manner when used in complex formation. However, in this case the formation of a single complex enantiomer has been found to be favoured in solution, provided the ligand molecule is synthesised such that the two chiral centres had the same relative stereochemistry, i.e.…”

Localizing Perturbations of the Racemic Equilibria Involving Dipicolinate‐Derived Lanthanide(III) Complexes

“…The Ln(III) content of stock solutions was determined by complexometric titrations with a standardized solution of EDTA in the presence of 0.1M ammonium acetate and aqueous arsenazo(III). 44 The synthesis of ADPA was performed with a minor deviation from a literature procedure. 45 Melting point measurements were performed on a Thermo Scientific Electrothermal MEL-TEMP 3.0.…”