Luminescent Dendrimers as Ligands and Sensors of Metal Ions - Advanced Fluorescence Reporters in Chemistry and Biology - page 254

Fig. 1 Schematic
representation of a dendrimer
and surface (Fig. 1 ). A most important feature of dendrimer chemistry is
the possibility of inserting selected chemical units in predetermined sites of the
dendritic architecture. Moreover, thanks to their three-dimensional structure,
internal dynamic cavities are present, where ions or molecules can be hosted. It is
thus possible to construct large nanoobjects capable of performing complex func-
tionality that derives from the integration of the specific properties of the constitu-
ent moieties. Nowadays both chemistry and physics of dendritic molecules are
rapidly expanding for fundamental research as well as for technological applica-
tions [ 2 ].
When the functional units incorporated into the dendrimers are luminescent,
information on dendrimer structure and properties can be gained by luminescence
studies. Indeed, a large number of chromophores can be arranged according to
predetermined patterns in a restricted space. Therefore, coupling luminescence and
dendrimer chemistry can lead to interesting photophysical properties [ 3 ], such as
(1) interactions of the dendritic luminescent units in the ground and/or in the excited
states (possible formation of excimers and/or exciplexes), (2) quenching of den-
drimer luminescence by external species, and (3) sensitization of luminescent metal
ions or dyes encapsulated by the dendrimer. Indeed, luminescent dendrimers have
been extensively investigated in the last few years both from a fundamental
viewpoint (e.g., theoretical studies on energy transfer processes [ 4 ], fluorescence
at the single molecule level) [ 5 ] and a variety of applications, including (1) light
harvesting [ 6 ], (2) changing the “color” of light [ 7 ], (3) sensing with signal
amplification [ 8 ], and (4) quenching and sensitization processes [ 9 ].
If dendrimers contain both luminescent units and coordination sites, they can
perform as luminescent ligands for metal ions [ 10 ]. Coupling luminescence with
metal coordination can indeed be exploited for a variety of purposes that include
investigation of dendrimer structures [ 11 ], encapsulated metal nanoparticles [ 12 ],