Cyclam-based dendrimers as ligands for lanthanide ions.
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.
Saudan
Christophe
C
Dipartimento di Chimica G. Ciamician, Universita di Bologna, via Selmi 2, I-40126 Bologna, Italy.
Ceroni
Paola
P
Vicinelli
Veronica
V
Maestri
Mauro
M
Balzani
Vincenzo
V
Gorka
Marius
M
Lee
Sang-Kyu
SK
van Heyst
Jeroen
J
Vögtle
Fritz
F