Chemistry Reference
In-Depth Information
FIGURE 9.17
Schematic representation of a photosynthetic unit [68].
dendrimers that mimic the light-harvesting ability of the PU [73]. The globular shape
of a dendrimer provides a large surface that can be functionalized with light-capturing
chromophores, which then transferred the absorbed energy toward the core. Electro-
active unit could then be placed at the core to finish the final step of the artificial
photosynthesis. However, the application of light-harvesting (LH) dendrimers is not
limited to energy conversion. As mentioned in the last section, LH dendrimer with
highly fluorescent cores could be used in OLED devices [31]. In addition, LH
dendrimers could also serve as highly sensitive molecular sensors due to its inherent
signal amplification ability [74]. Other potential applications include nonlinear
optics [75].
9.3.1.2 Why Use Shape-Persistent Conjugated Dendrimers as LH Materials
Considerable amount of work has been reported on light-harvesting dendrimers
using aliphatic or so-called “flexible” linkage, especially on the Fr
echet-type
dendrons [68,76-78]. However, shape-persistent LH dendrimers have some unique
properties in comparison with flexible ones.
First, a rigid scaffold helps to pin down the distance and relative orientation of the
transition dipoles of donor and acceptor. This makes theoretical modeling and precise
design possible. In nature, the exact allocation of chromophores relies on the well-
defined 3-D structure of protein matrix [70]. Here, the rigid dendrimer scaffold is
expected to function similarly. Second, in shape-persistent LH dendrimers, both
Dexter [79] and Forster [80] energy transfer (ET) mechanism might operate,
depending on the exact molecular structure. In flexible dendrimers, disrupted
conjugated system precludes the Dexter ET mechanism, which requires orbital
