Electron antennae

Electrodes that featured a submonolayer (-15% of a monolayer) of 12 nm diameter Au colloids exhibited reversible cyt c voltammetry at scan rates of 50, 100, 200, and 500 mV s (Figure 13.3). Au particles in the submonolayer films can be thought of as electron antennae , efficiently funnel-ing electrons between the electrode and the electrolyte. However, the authors also reported a wide variation in voltammetric responses, with peak-to-peak separations ranging from 60 to 115 mV, among several similarly prepared electrodes. The heterogeneous rate constant calculated from the dependence of the peak-to-peak separation on scan rate was 7 x 10 cm s", which is in agreement with previously reported measurements obtained with bulk material electrodes. ... 

In this volume of the Handbook the authors sample the gamut of rare-earth-element involvement on the planet. From the magnetic characteristics of atomic nuclei, to the electronic antenna effects of ligands on encapsulated atoms, to the effects on spectral properties of neighboring atoms in a crystalline array, to the chemical combination of the rare-earth elements with phosphorus, to the chemical constitution of vapor species of their halides, to the distribution of these elements in the waters that envelope the earth. 

With tlie development of femtosecond laser teclmology it has become possible to observe in resonance energy transfer some apparent manifestations of tire coupling between nuclear and electronic motions. For example in photosyntlietic preparations such as light-harvesting antennae and reaction centres [32, 46, 47 and 49] such observations are believed to result eitlier from oscillations between tire coupled excitonic levels of dimers (generally multimers), or tire nuclear motions of tire cliromophores. This is a subject tliat is still very much open to debate, and for extensive discussion we refer tire reader for example to [46, 47, 50, 51 and 55]. A simplified view of tire subject can nonetlieless be obtained from tire following semiclassical picture. 

The Maxwell theory of X-ray scattering by stable systems, both solids and liquids, is described in many textbooks. A simple and compact presentation is given in Chapter 15 of Electrodynamics of Continuous Media [20]. The incident electric and magnetic X-ray helds are plane waves Ex(r, f) = Exo exp[i(q r — fixO] H(r, t) = H o exp[/(q r — fixO] with a spatially and temporally constant amplitude. The electric field Ex(r, t) induces a forced oscillation of the electrons in the body. They then act as elementary antennas emitting the scattered X-ray radiation. For many purposes, the electrons may be considered to be free. One then finds that the intensity /x(q) of the X-ray radiation scattered along the wavevector q is... 

Langa and co-workers have prepared fullerodendrimers 18 and 19 in which the phenylenevinylene dendritic wedge is connected to a pyrazoHno [60] fullerene core rather than to a fulleropyrrolidine one as for 12-17 (Fig. 9) [44]. Preliminary photophysical investigations suggest that the efficient energy transfer from the excited antenna moiety to the pyrazolino [60] fullerene core is followed by an electron transfer involving the fullerene moiety and the pyrazoHne N atom. 

Square-planar zinc compounds predominate with these ligand types as would be predicted. This is in contrast to the prevalence of tetrahedral or distorted tetrahedral geometries for four-coordinate species that have been discussed thus far. Zinc porphyrin complexes are frequently used as building blocks in the formation of supramolecular structures. Zinc porphyrins can also act as electron donors and antenna in the formation of photoexcited states. Although the coordination of zinc to the porphyrin shows little variation, the properties of the zinc-coordinated compounds are extremely important and form the most extensively structurally characterized multidentate ligand class in the CSD. The examples presented here reflect only a fraction of these compounds but have been selected as recent and representative examples. Expanded ring porphyrins have also... 

The photoactive properties and potential for use of some of these compounds as photoactive antennas have been explored. Electron transfer studies between C60 fullerene and zinc porphyrins... 

FIGURE 7.3 Structure of PSII membranes, macrocomplexes and LHCII antenna. Left from the top electron microscopy of grana stacks, PSII macrocomplexes, LHCII trimers, and LHCII oligomers. Right from the top Atomic structure of LHCII monomer (I and II are side and top views). Bottom part displays LHCII... 

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