Luminescent Lanthanide Ions Hosted in a Fluorescent Polylysin Dendrimer. Antenna-Like Sensitization of Visible and Near-Infrared Emission

• Published in: Journal of the American Chemical Society 2002-06, Vol.124 (22), p.6461-6468
• Main Authors: Vicinelli, Veronica, Ceroni, Paola, Maestri, Mauro, Balzani, Vincenzo, Gorka, Marius, Vögtle, Fritz
• Format: Article
• Language: English
• Subjects: Atomic and molecular physics; Exact sciences and technology; Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion); Molecular properties and interactions with photons; Physics; Radiationless transitions, quenching
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja017672p

We have investigated the complexation of the luminescent Nd3+, Eu3+, Gd3+, Tb3+, Er3+, and Yb3+ 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 Nd3+, Er3+, and Yb3+, 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 Nd3+ or Eu3+, 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 Eu3+ 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.