Energy Transfer in Supramolecular Heteronuclear Lanthanide Dimers and Application to Fluoride Sensing in Water

Abstract

In the presence of fluoride anions, [LnL(H O)] complexes, based on the coordination of a lanthanide (Ln) cation into the cavity of a C symmetrical cyclen-based ligand (L), self-assemble in water to form [(LnL) F] dimers. The crystal structures of the Yb hydrated monomer and of the fluorinated dimer are reported and analyzed to unravel the impact of the cumulative effect of weak hydrogen bonding and aromatic stacking interactions in the supramolecular assembly. The assembly is stable over a broad range of pH 3-8. A combination of equimolar amounts of Eu and Tb complexes led to a quasistatistical mixture of homo- and heterodimers, as observed by using electrospray mass spectrometry. In the heterodimers, selective excitation into the F → D absorption band of the Tb center at λ=488 nm allowed the observation of a Tb-to-Eu downshifting energy transfer, not observed in the absence of fluoride ions. Analysis of the excited-state lifetimes of the dimers within the frame of the Förster theory of energy transfer showed the transfer to have an efficiency of 34 %, with a corresponding Förster radius of 4.1 Å; thereby, unraveling the short Ln-Ln distance as a crucial parameter of the energy-transfer process. By using equimolar mixtures of the Tb and Eu complexes, the energy-transfer phenomenon was used for a ratiometric sensing of fluoride anions in water with a detection limit of 17.7 nm.

Probing Optical Anisotropy and Polymorph‐Dependent Photoluminescence in [Ln2] Complexes by Hyperspectral Imaging on Single Crystals

“…Short Ln⋅⋅⋅Ln distance as a crucial parameter for efficient energy transfer in Ln dimers has recently been reported, which perfectly aligns with our observations. According to the crystallographic data of 3 a (Table S1), not only the unit cell parameters along the a‐ and b‐axes are smaller than that of the c‐axis, but also the shortest intermolecular Ln⋅⋅⋅Ln distances are observed within the plane formed by the a and b axes, namely the (0 0 1) face (7.22 and 7.43 Å, Figure S1).…”

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.…”

A stoichiometric terbium-europium dyad molecular thermometer: energy transfer properties

“…The antenna effect of the chelating chromophore, which possesses a large absorption cross section, allows more incident light to be absorbed and transferred to a lanthanide ion, making such complexes brighter than most lanthanide-doped inorganic nanocrystals. Unsurprisingly, few literature reports 18 , 21 include an investigation of the energy transfer processes using lanthanide hetero-dinuclear complexes - and even then with the co-presence of homo-dinuclear species in the complex mixture. Even though great effort has been expended to synthesize pure hetero-polynuclear complexes 22 , 23 with different chemically similar lanthanide ions, there remains a considerable need for a simple strategy for controlling the formation of hetero-dinuclear complexes.…”