Luminescent Dendrimers as Ligands and Sensors of Metal Ions - Advanced Fluorescence Reporters in Chemistry and Biology - page 278

[Ru(bpy) 2 (CN) 2 ]toNd 3+ can be assumed to be equal to the efficiency of the
quenching of the [Ru(bpy) 2 (CN) 2 ] emission (ca. 90%) because quenching by
electron transfer can be ruled out in view of the Nd 3+ redox properties. No evidence
of energy transfer in the adduct from the naphthyl-localized T 1 excited state of the
dendrimer to the lowest 3 MLCT state of [Ru(bpy) 2 (CN) 2 ] has been found since no
change in the T 1 lifetime at 77 K has been observed.
The three components of the self-assembled structure have complementary
properties, so that new functions emerge from their assembly. Dendrimer 2 has a
very high molar absorption coefficient in the UV spectral region because of 12
dimethoxybenzene and 16 naphthyl units, but it is unable to sensitize the emission
of a Nd 3+ ion placed in its cyclam core. The [Ru(bpy) 2 (CN) 2 ] complex can coordi-
nate (by the cyanide ligands) and sensitize the emission of Nd 3+ ions. Self-assembly
of the three species leads to a quite unusual Nd 3+ complex which exploits a
dendrimer and a Ru 2+ complex as ligands. Such a system behaves as an antenna
that can harvest UV to VIS light absorbed by both the Ru 2+ complex and the
dendrimer and emit in the NIR region with line-like bands. In principle, the
emission wavelength can be tuned by replacing Nd 3+ with other lanthanide ions
possessing low-lying excited states.

4 Conclusions

The above discussed examples show that the design of dendrimers capable of
playing the role of ligands for metal ions can lead to novel classes of metal
complexes where the properties of the dendrimer and metal ion moieties can be
profitably combined to obtain interesting and useful light-related functions that
reflect the occurrence of intercomponent energy and electron transfer processes. It
is likely that improving the design of these types of dendrimers will lead to
coordination compounds capable of performing even more sophisticated functions,
such as energy up-conversion, electrochemiluminescence, and light emitting diodes
(LED), besides those discussed in this paper.

References

1. (a) V¨gtle F, Richardt G, Werner N (2009) Dendrimer chemistry. Wiley-VCH, Chichester
(b) Newkome GR, V¨gtle F (2001) Dendrimers and dendrons. Wiley-VCH, Weinheim
(c) Fr ´ chet JMJ, Tomalia DA (2001) Dendrimers and other dendritic polymers. Wiley,
Chichester
2. For some reviews, see: (a) Majoral J-P (2007) Influence of cationic phosphorus dendrimers on
the surfactant-induced synthesis of mesostructured nanoporous silica. New J Chem
31:1259-1263 (b) Puntoriero F, Nastasi F, Cavazzini M et al (2007) Coupling synthetic
antenna and electron donor species: a tetranuclear mixed-metal Os(II)-Ru(II) dendrimer
containing six phenothiazine donor subunits at the periphery. Coord Chem Rev