Chemistry Reference
In-Depth Information
2
is the orientation factor, J
is the overlap integral of the fluorescence intensity of the donor and the molar
extinction coefficient of the acceptor normalized by the frequency expressed in
wavenumbers, n is the index of refraction of the solvent, and Q
0
is excitation
quantum efficiency of the donor.
Precise design of the luminescent property requires the fine geometry of these
chromophors in the solid state. Even if the luminescent film is composed of a
mixture of several chromophors, the dendrimer architecture can produce a well-
defined intermolecular distance allowing the precise control of through space
(FRET) or through bond energy transfer [152-154]. We can also take advantage of
the highly regulated nanostructure to optimize the photochemical processes in
photovoltaic devices. The charge-separating reaction upon the photoexcitation of
the chromophor is a well-established process as the initial reaction during
photosynthesis. The photoexcitation is not direct, but transmitted through a
light-harvesting antenna that is composed of a multiple P850 cytochrome placed
near the center (Figure 10.14). Stacking of an organic and metal complex
chromophor in close proximity can be achieved by the dendrimer synthesis. The
maximum energy transduction in a multiporphyrin system is achieved by the
oligomeric structure based on the dendrimer topology. At the topology level,
the dendrimer architecture is suitable for collecting the photoexcitation energy
because the core unit is located at the focal point [155-164]. At the geometry level,
the summation of the distances between the core and every terminus is minimized if
the symmetric multidendronized core, which leads to a core-centered model, was
used. Several experimental results showed that a close-packing dendrimer archi-
tecture enables complete repression of the energy loss [108].
where r is distance between the donor and acceptor,
k
FIGURE 10.14
Molecular 3-D coordination structures of metalloproteins playing an im-
portant role in the photosynthetic reaction center. Each picture is based on a crystal structure,
visualizing only its functional components without any protein. (Right) Light-harvesting
complex from Rhodopseudomonas acidophila (pdb code: 1kzu) [191]. The photosynthetic
reaction center from Rhodopseudomonas viridis (pdb code: 2prc) [192]. (See the color version
of this figure in Color Plates section.)
