title: Optimization of the Sensitization Process and Stability of Octadentate Eu(III) 1,2-HOPO Complexes.
abstract: The synthesis of a series of octadentate ligands containing the 1-hydroxypyridin-2-one (1,2-HOPO) group in complex with europium(III) is reported. Within this series, the central bridge connecting two diethylenetriamine units linked to two 1,2-HOPO chromophores at the extremities (5-LIN-1,2-HOPO) is varied from a short ethylene chain (H(2,2)-1,2-HOPO) to a long pentaethylene oxide chain (H(17O5,2)-1,2-HOPO). The thermodynamic stability of the europium complexes has been studied and reveals these complexes may be effective for biological measurements. Extension of the central bridge results in exclusion of the inner-sphere water molecule observed for [Eu(H(2,2)-1,2-HOPO)](-) going from a nonacoordinated to an octacoordinated Eu(III) ion. With the longer chain length ligands, the complexes display increased luminescence properties in aqueous medium with an optimum of 20% luminescence quantum yield for the [Eu(H(17O5,2)-1,2-HOPO)](-) complex. The luminescence properties for [Eu(H(14O4,2)-1,2-HOPO)](-) and [Eu(H(17O5,2)-1,2-HOPO)](-) are better than that of the model bis-tetradentate [Eu(5LIN(Me)-1,2-HOPO)2](-) complex, suggesting a different geometry around the metal center despite the geometric freedom allowed by the longer central chain in the H(mOn,2) scaffold. These differences are also evidenced by examining the luminescence spectra at room temperature and at 77 K and by calculating the luminescence kinetic parameters of the europium complexes.
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720-1460, United States.|Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
authors.forename: Anthony
authors.initials: A
authors.lastname: D'Aléo
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720-1460, United States.|Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
authors.forename: Evan G
authors.initials: EG
authors.lastname: Moore
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720-1460, United States.|Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
authors.forename: Jide
authors.initials: J
authors.lastname: Xu
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720-1460, United States.|Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
authors.forename: Lena J
authors.initials: LJ
authors.lastname: Daumann
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720-1460, United States.|Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
authors.forename: Kenneth N
authors.initials: KN
authors.lastname: Raymond
mesh_terms: D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D005063:Europium / Q000737:chemistry*; D008024:Ligands; D049408:Luminescent Agents / Q000138:chemical synthesis / Q000737:chemistry*; D008958:Models, Molecular; D011728:Pyridones / Q000138:chemical synthesis / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: C580946:1,2-hydroxypyridinone; D056831:Coordination Complexes; D008024:Ligands; D049408:Luminescent Agents; D011728:Pyridones; D005063:Europium