Cross-antenna

With analogy to electric circuits, a transfer function of the antenna can be calculated and the response of the antenna to an incoming wave obtained. The output signal is usually expressed as antenna cross-section. It is defined as the ratio between the total energy absorbed by the antenna and the incident spectral density function of the incident wave. In the case of Nautilus antenna (2300 kg, 3 x 0.6 m) the cross-section is of the order of 10 25m2 Hz. 

I. P. Theron, E. K. Walton, and S. Gunawan, Compact range radar cross-section measurements using a noise radar , IEEE Trans. Antennas Propagat., vol. 46, pp. 1285-1288, Sept. 1998. 

The first issue can be addressed in two ways a primary ET species which has a large optical absorption cross-section can be chosen or arrays of molecules with large optical absorption cross-sections can be used as "antennas" that will efficiently collect and transport the electronic excitation energy to the primary ET species, in direct analogy to photosynthetic systems. While in the latter case it should be possible to develop systems with more efficient solar photon collection, the number of primary ET species will have to be reduced due to the spatial limitations, which will also reduce the potential electric current that can be produced by the system. Thus, questions related to the detailed molecular architecture of biomimetic solar energy conversion devices will have to address this issue, and it is quite likely that a number of compromises will have to be made before optimal design characteristics are obtained. 

The low absorption cross-sections of the trivalent ions means that an indirect method of populating the metal excited states is required to generate a significant emission. Such a mechanism is the Antenna Effect. 

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]. 

Gust and co-workers designed a synthetic antenna reaction center capable of undergoing energy transfer followed by electron transfer.11461 Four ZnP chromo-phores are covalently linked to a FBP electron donor, forming a cross, and the FBP is in turn attached to a C60 electron acceptor (compound 27). Excitation of a ZnP... 

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