Antenna natural

Artificial and natural antennae Migration of excitation energy... 

The study of artificial photosynthesis has been the subject of ongoing attention for many years now due to the need for sustainable energy resources. In natural photosynthesis a lightharvesting antenna system with a large optical cross-section (for example the LH2 complex) absorbs a photon that is funneled by energy transfer (ET) to the reaction centre [1-3]. Excellent candidates to mimic the natural antenna system are molecules that efficiently absorb light and are able to transfer the captured energy to other parts of the molecule. Molecules based on Zn and free-base porphyrins are examples of compounds that can be used as models for the LID complex [4]. 

Hofkens J, Schroeyers W, Loos D, et al. Triplet states as non-radiative traps in multi-chromophoric entities single molecule spectroscopy of an artificial and natural antenna system. Spectrochim Acta 2001 A57 2093-107. 

The aim of this article is to discuss the basic requirements that an antenna system has to fulfill and to summarize some examples of the various artificial antennas reported in the literature. For the sake of comparison, brief comments on natural antennas are also presented. 

Because Nature elected porphyrin derivatives as components of the natural antennas, it cannot be surprising that many artificial antennas are based on these chromophores. This represents surely the largest class of artificial antennas studied. Even for this class, we discuss just a few representative examples [28]. 

Carbonera D, Di Valentin M, Agostini G, Giacometti G, Liddell PA, Gust D, Moore AL and Moore TA (1997b) Energy transfer and spin polarization ofthe carotenoid triplet state in synthetic carotenoporphyrin dyads and in natural antenna complexes. Appl Magn Res 13 487-504... 

Figure 13.38. A dodecameric porphyrin wheel closely resembles natural antennae systems in terms of the number of chromophores.

In a crystal of identical chromophores, for example, a naphthalene crystal, local excitations may be transferred to other sites, just like electrons or holes. Excitation energy transfer (EET) is also called electron-hole pair transfer because the excited electron and remaining hole are transferred simultaneously to the other atom or molecule. Degeneracy appears in a finite system with two identical chromophores. In a repetitive system, the excitations may be delocalized, but this is not always the case. Devices for solar light harvesting, and natural antenna systems are examples of such repetitive systems. It is important to understand their properties. 

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