title: Cyclam-based dendrimers as ligands for lanthanide ions.
abstract: We have investigated the complexation of lanthanide ions (Nd3+, Eu3+, Gd3+, Tb3+, Dy3+) with three cyclam-based ligands (cyclam = 1,4,8,11-tetraazacyclotetradecane), namely 1,4,8,11-tetrakis(naphthylmethyl)cyclam (1), and two dendrimers consisting of a cyclam core appended with four dimethoxybenzene and eight naphthyl units (2) and twelve dimethoxybenzene and sixteen naphthyl units (3). In the free ligands the fluorescence of the naphthyl units is strongly quenched by exciplex formation with the cyclam nitrogens. Complexation with the metal ions prevents exciplex formation and revives the intense naphthyl fluorescence. Fluorescence and NMR titration experiments have revealed the formation of complexes with different metal/ligand stoichiometries in the case of 1, 2 and 3. Surprisingly, the large dendrimer 3 gives rise to a stable [M(3)3]3+ species. Energy transfer from the lowest singlet and triplet excited states of the peripheral naphthyl units to the lower lying excited states of Nd3+, Eu3+, Tb3+, Dy3+ coordinated to the cyclam core does not take place.
authors.affiliation: Dipartimento di Chimica G. Ciamician, Universita di Bologna, via Selmi 2, I-40126 Bologna, Italy.
authors.forename: Christophe
authors.initials: C
authors.lastname: Saudan
authors.forename: Paola
authors.initials: P
authors.lastname: Ceroni
authors.forename: Veronica
authors.initials: V
authors.lastname: Vicinelli
authors.forename: Mauro
authors.initials: M
authors.lastname: Maestri
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Balzani
authors.forename: Marius
authors.initials: M
authors.lastname: Gorka
authors.forename: Sang-Kyu
authors.initials: SK
authors.lastname: Lee
authors.forename: Jeroen
authors.initials: J
authors.lastname: van Heyst
authors.forename: Fritz
authors.initials: F
authors.lastname: Vögtle