M. Zhou et J. Roovers, Dendritic supramolecular assembly with multiple Ru(II) tris(bipyridine) units at the periphery: Synthesis, spectroscopic, and electrochemical study, MACROMOLEC, 34(2), 2001, pp. 244-252
A supramolecular assembly with eight peripheral ruthenium(II) tris(bipyridi
ne), [RU(bpy)(3)](2+) units covalently linked to a carbosilane dendrimer pl
atform has been synthesized. H-1 NMR and MALDI-TOF mass spectrometry confir
m the target structure. Spectroscopic and electrochemical studies disclose
that the identical [Ru(bpy)(3)](2+) units in this system interact neither i
n the ground state nor in the excited state. In acetonitrile solutions of i
dentical molar concentration of [Ru(bpy)(3)](2+) units, both the dendrimer
and reference monomeric [Ru(bpy)(2)(4-octoxy-2,2'-bipyridine](2+) exhibit i
dentic al absorption and emission spectra. Cyclic voltammetry reveals that
the dendrimer and monomer possess the same redox potentials of the metal-ce
ntered oxidation process [RU(bpy)(3)](2+/3+) and the first ligand-centered
reduction process [RU(bpy)(3)](1+/2+). The abnormal redox peaks of the [RU(
bpy)3](0/1+) and [RU(bpy)(3)](1-/0) transitions of the dendrimer are attrib
uted to the accumulation of neutral dendrimer on the electrode. A prelimina
ry study of the electrochemiluminescence (ECL) in tripropylamine-acetonitri
le solution indicates that the ECL intensity of the dendrimer with eight [R
U(bpy)(3)](2+) units is 5 times higher than that of the reference monomeric
species. Therefore, the molar emission, generated either by photoexcitatio
n or by electrochemical excitation, can be amplified by incorporating multi
ple luminophores into a multibranch platform without significantly changing
the redox and photophysical properties. The possible use of supramolecular
assemblies as labels for biodiagnostics is discussed.