Antenna system

The first antenna system (or light-harvesting complex) to be structurally determined belongs to purple bacteria (Cogdell et al., 1995). The remarkable fact with this antenna system is that it has evolved into circular shapes containing a certain number of identical chromophores. 

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Kranss, N., et al., 1996. Photosystem I at 4 A resolution represents the first structural model of a joint photosynthedc reaction centre and core antenna system. Nature Structural Biology 3 965-973. 

Very interesting antenna systems have been constructed by functionalizing the chain ends of a poly(arylether) convergent dendritic backbone with cou-marin-2 A =435 nm) and its focal point with coumarin-343 X =49Q nm) [33] dendrimer 8 represents the fourth generation. 

Neoxanthin and the two lutein molecules have close associations with three transmembrane helixes, A, B, and C, forming three chlorophyll-xanthophyll-protein domains (Figure 7.5). Considering the structure of LHCII complex in terms of domains is useful for understanding how the antenna system works, and the functions of the different xanthophylls. Biochemical evidence suggests that these xanthophylls have a much stronger affinity of binding to LHCII in comparison to violaxanthin... 

Light is concentrated by a factor of V300 by use of an extensive antenna system of pigments. This minimizes the need to duplicate reaction centers. 

Keywords Molecular Devices a Molecular Machines a Molecular Wires a Antenna Systems a Molecular Switches a Plug/socket Systems a Pseudorotaxanes a Rotaxanes a Catenanes a Supramolecuiar Chemistry a Photochemistry a Electrochemistry a Luminescence... 

His research interests deal with the chemistry of cyclopropane derivatives, 1,3-dipolar cycloadditions, synthesis of natural compounds and biologically active analogues. Recently, the research activity is also dedicated to synthetic studies for the production of new materials light-harvesting antenna systems and functionalized organogelators. 

Sunlight is efficiently absorbed throughout the solar spectrum by an antenna system containing bacteriochlorophyll and carotenoid chromophores in a protein environment. 

May V (2009) Beyond the Forster theory of excitation energy transfer importance of higher-order processes in supramolecular antenna systems. Dalton Trans 45 10086-105... 

Finally, energy migration, i.e. excitation energy hopping, in polymers, artificial antenna systems, photo synthetic units, etc. can be investigated by fluorescence polarization (see Chapter 9). 

This chapter shows that zeolite L is a very suitable host for the arrangement of a wide variety of chromophores. The structure of zeolite L is such that the formation of non-fluorescent dimers inside the channels can be prohibited and chromophores can be aligned in a certain direction. We have shown that this host-guest system can be used to make very efficient nanoscale two-directional photonic antenna systems. A broad spectral absorption range can be achieved by using several different cationic and neutral dyes. 

It is a challenge to couple the antenna systems to a device (e.g., a semiconductor). It has already been shown that it is possible to prepare organized zeolite monolayers on flat surfaces [78, 79]. For coupling, the interface between the chromophore loaded zeolite L antenna systems and the semiconductor becomes very important. Stopcock molecules are expected to function as a bridge between the chromophores in the zeolite L channels and the device surface, which will open a whole new exciting research area. The first successful experiments with slopcock modified crystals have been reported recently [80]. 

Table 1. Pigment-proteins of the PSII antenna system from higher plants...

Pairwise EET rates cannot be directly measured in antenna systems. The closest approach to direct determination is offered on the one hand by time resolved picosecond and sub-picosecond absorption and fluorescence measurements and on the other hand by hole burning spectroscopies. Time resolved techniques do not detect transfer between isoenergetic sites. A somewhat more indirect approach to determining pairwise rates is that of analysing excited state lifetime data in terms of a particular antenna and an EET model. 

In monodirectional antenna systems, the energy is transported in one direction only. We discuss the possibilities sketched in Fig. 22 to create asymmetrical... 

Figure 27 Sensitized solar cell based on dye-loaded zeolite L antenna systems. The antenna systems absorb light and transport their energy mainly along the c axis of the crystals to the semiconductor surface. Electron-hole pairs are formed in the semiconductor by energy transfer from the antenna system to the conduction band of the semiconductor.

Figure 28 Tandem solar cell where monodirectional antenna systems with three dyes are put between two w-type semiconductors with different hand gaps.

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