Spectroscopic Properties of a Family of Mono‐ to Trinuclear Lanthanide Complexes

Abstract

International audienceA series of mono-, di-, and trinuclear complexes of Eu and Tb was designed to study the influence of the number of Ln emitting centers on the luminescence properties of discrete polynuclear complexes. The complexes are based on a cyclen scaffold, functionalized by two picolinic acid pendant arms. These coordinating units are separated by a 1,3-dimethylbenzene spacer for the dinuclear complex and a 1,3,5-trimethylbenzene bridge in the case of the trinuclear complex. The synthesis and characterization of the ligands are presented, together with the preparation and spectroscopic characterization of the complexes. The luminescence properties of the complexes were determined by UV/Vis absorption spectroscopy and steady-state and time-resolved luminescence spectroscopy in buffered aqueous solutions. Comparison of the electronic absorption spectra showed that the absorption properties can almost be considered as extensive parameters within experimental error, as expected for electronically non-conjugated systems. A small drop of both the excited state luminescence lifetimes and the luminescence quantum yields was observed for the trinuclear complexes in the case of Tb. To understand this behavior, theoretical HF (Hartree-Fock) calculations were performed for the three complexes. Models indicate that the average intermetallic distance in the dinuclear complex is almost the same as in the trinuclear one, disfavoring a possible distance dependence of the observed phenomena

Pyclen-Based Ligands Bearing Pendant Picolinate Arms for Gadolinium Complexation

“…The absorption spectra of the [Tb L5 ] + and [Tb L6 ] + complexes present an absorption maximum at 269 nm (ε ≈ 9800 M –1 cm –1 ) typical of the picolinate chromophore (Figure S35 in the Supporting Information). , The emission spectra recorded upon excitation in the ligand bands (272 nm) show the typical 5 D 4 → 7 F J transitions of Tb­(III), which are observed at ca. 490 ( J = 6), 544 ( J = 5), 583 ( J = 4), and 621 ( J = 3) nm (Figure ).…”

Formation of Heteropolynuclear Lanthanide Complexes Using Macrocyclic Phosphonated Cyclam-Based Ligands

“…9,10,11,12,13 Indeed their unique hierarchical energy levels render them attractive candidates in this regard, as both donors and acceptors of energy, and it has previously been shown that efficient molecular inter-lanthanide energy transfer occurs in both homonuclear 14,15 and heteronuclear complexes. 16,17,18 The synthesis of homopolynuclear lanthanide complexes has been explored for a range of conventional multi-chelating ligands, 19,20,21,22 in addition to supramolecular architectures based upon helicates, 23,24,25 expanded macrocycles, 26 coordination cages, 27,28 and other synergistic weak interactions. 29 Conversely, the accessibility of covalent heteropolymetallic trivalent lanthanide complexes is challenging due to the comparable chemical properties and hence reactivity across the period, distinguishable only in their ionic radii with minute change in preferred coordination numbers and geometries.…”

“…The synthesis of homopolynuclear lanthanide complexes has been explored for a range of conventional multichelating ligands, − in addition to supramolecular architectures based upon helicates, − expanded macrocycles, coordination cages, , and other synergistic weak interactions . Conversely, the accessibility of covalent heteropolymetallic trivalent lanthanide complexes is challenging due to the comparable chemical properties and hence reactivity across the period, distinguishable only in their ionic radii with minute change in preferred coordination numbers and geometries.…”

Expanding the Family of Pyclen-Based Ligands Bearing Pendant Picolinate Arms for Lanthanide Complexation

“…Given the potentially nonadentate nature of ligands L3 and L4 , and the results obtained for their Y 3+ complexes, we hypothesized that these ligands should present interesting complexation properties for the Ln 3+ ions. Furthermore, picolinate groups are known to provide a rather efficient sensitization of the emission of Eu 3+ and especially Tb 3+ , which emit in the visible region of the spectrum. ,, Thus, in this paper we present the fourth chapter on Y 3+ and/or Ln 3+ complexes with this series of ligands that combine three main elements: pyclen, picolinate, and acetate arms. We report a detailed investigation of the structures of the Ln 3+ complexes of L3 and L4 in the solid state and in solution.…”