The Beauty of Chemistry in the Words of Writers and in the Hands of Scientists - Beauty in Chemistry - page 87

excitation of the Ru-based unit of 7 2 þ is followed by electron transfer to 9 2 þ , with
8H þ playing the role of an extension cable (Fig. 9b ). The occurrence of this process
is confirmed by nanosecond-laser flash-photolysis experiments, showing a transient
absorption signal assigned to the 4,4 ' -bipyridinium radical cation formed by pho-
toinduced electron transfer within the self-assembled triad. Interestingly, the exten-
sion cable component 8H þ exists in a self-threaded conformation [ 60 ], that cannot
host the electron drain until it is opened up by complexation with the socket unit of
the source component. This feature, which can be viewed as a limitation because it
reduces the efficiency, in fact plays the function of a safety-catch device. Moreover,
the photoinduced electron-transfer process can be powered by sunlight because the
7 2 þ [Ru(bpy) 3 ] 2 þ -type component shows a broad and intense absorption band in the
visible spectral region.
7.3 Dendrimers: Appealing Structures and Useful Compounds
Highly branched molecules having tree-like structures are called dendrimers from
the Greek word dendron (Fig. 10 ). Like trees, dendrimers usually exhibit estheti-
cally pleasant structures, but they are more interesting if they are able to produce
“fruit,” i.e., to perform useful functions.
7.3.1 Light-Harvesting Antennas
In the last 10 years, much attention has been devoted to the design and synthesis of
dendrimers [ 61 , 62 ] capable of playing the role of antennas (Fig. 11 ) in artificial
Fig. 10 Dendrimers are highly branched molecules with a tree-like structure