Jean-Claude Bunzli - Luminescent Lanthanide Helicates Self-Assembled from Ditopic Ligands Bearing Phosphonic Acid or Phosphoester Units

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      Publication Details (including relevant citation   information):

      Chauvin,A.S., Comby,S., Baud,M., De Piano,C., Duhot,C.,   Bunzli,J.C.G. Inorganic Chemistry 2009  48 (22) 10687-10696

      Abstract: A series of hexadentate ditopic   receptors incorporating benzimidazole moieties have been   designed, which are fined with phosphonic acid or   phosphoethylester coordinating units. In addition,   poly(oxyethylene) pendants have been introduced on the   benzimidazole backbone of two ligands to increase water   solubility. The ligands self-assemble with lanthanide ions under   stoichiometric conditions, yielding triple-stranded   homobimetallic helicates, as ascertained by mass spectrometry and   UV-visible titrations. The helicates display large thermodynamic   stability, for example, log beta(23) approximate to 21-24 for all   the Eu(III) complexes. Photophysical measurements reveal   sensitization of the metal-centered luminescence in the europium   and terbium complexes, which is modulated by the nature of the   ligand. Hydration numbers determined by the lifetime method are   essentially zero. The Eu((5)D(0)) lifetimes are long and reach   values up to 3.2 ms, while quantum yields as high as 25% are   obtained in water at pH 7.4. Back transfer limits the   sensitization efficiency for Tb(III) luminescence, and both   lifetimes and quantum yields are much smaller. The properties of   the helicates are discussed with respect to those self-assembled   from ligands bearing carboxylate coordinating units

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