In a fourth generation poly(propylene amine) dendrimer decorated with 32 dansyl units at the periphery and containing 30 aliphatic amine units in the interior, the strong fluorescence of all the dansyl units is quenched when a Co 2+ ion is incorporated into the dendrimer.
We have investigated the complexation of the luminescent Nd(3+), Eu(3+), Gd(3+), Tb(3+), Er(3+), and Yb(3+) ions by a polylysin dendrimer containing 21 amide groups in the interior and, in the periphery, 24 chromophoric dansyl units which show an intense fluorescence band in the visible region. Most of the experiments were performed in 5:1 acetonitrile/dichloromethane solution at 298 K. On addition of the lanthanide ions to dendrimer solutions, the fluorescence of the dansyl units is quenched; in Nd(3+), Er(3+), and Yb(3+), a sensitized near-infrared emission of the lanthanide ion is observed. At low metal ion concentrations, each dendrimer hosts only one metal ion and when the hosted metal ion is Nd(3+) or Eu(3+), the fluorescence of all the 24 dansyl units of the dendrimer is quenched with unitary efficiency. Quantitative measurements were performed in a variety of experimental conditions, including protonation of the dansyl units and measurements in rigid matrix at 77 K where a sensitized Eu(3+) emission could also be observed. The results obtained have been interpreted on the basis of the energy levels and redox potentials of dendrimer and metal ions.
Ein fleißiger Lichtsammler ist das Eosinmolekül, das im hier gezeigten Dendrimer eingeschlossen ist; es sammelt Energie von allen 64 Chromophoren des Dendrimers, von denen es drei verschiedene Arten gibt. Es erfolgt ein effizienter intramolekularer (d. h. innerhalb des Dendrimers) und intermolekularer Energietransfer (Dendrimer→Eosin) nach einem Förster‐artigen Mechanismus, was sich anhand der starken Überlappung der Emissions‐ und Absorptionsspektren der relevanten Donor‐ und Acceptor‐Einheiten bemerkbar macht.
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