Doping charge transfer systems

To search for new magnetic materials in C60-based charge-transfer systems, one needs to look for cases where Jahn-Teller-distorted orientationally ordered Qo ions occupy noncubic sites. It would be very interesting to test the magnetic properties of doped smaller fullerides, i.e., C with n<60, as one expects larger exchange couplings in these systems. Another direction would be to search... 

Electronic Raman scattering originates not only from free electron excitations, but also from collective electron excitations in the form of plasmons. So far, these two types of excitation have been observed only in conventional semiconductors and to some extent in high temperature superconductors, as discussed in subsections 4.8.4 and 4.8.5. However, doped polymers with not too high carrier concentrations or charge transfer systems are possible candidates, and the search for electronic Raman scattering in such systems is one of the challenges in this held. 

Finally, an interesting comparison can be performed between the influence of the charge transfer on the pinch mode in the doped fullerenes and its influence on the C=C stretching mode in conventional charge transfer systems (Figure 12). For the fulle-... 

For the alkali metal doped Cgo compounds, charge transfer of one electron per M atom to the Cgo molecule occurs, resulting in M+ ions at the tetrahedral and/or octahedral symmetry interstices of the cubic Cgo host structure. For the composition MaCgg, the resulting metallic crystal has basically the fee structure (see Fig. 2). Within this structure the alkali metal ions can sit on either tetragonal symmetry (1/4,1/4,1/4) sites, which are twice as numerous as the octahedral (l/2,0,0) sites (referenced to a simple cubic coordinate system). The electron-poor alkali metal ions tend to lie adjacent to a C=C double... 

An alternative approach to stabilizing the metallic state involves p-type doping. For example, partial oxidation of neutral dithiadiazolyl radicals with iodine or bromine will remove some electrons from the half-filled level. Consistently, doping of biradical systems with halogens can lead to remarkable increases in conductivity and several iodine charge transfer salts exhibiting metallic behaviour at room temperature have been reported. However, these doped materials become semiconductors or even insulators at low temperatures. 

The oscillations observed with artificial membranes, such as thick liquid membranes, lipid-doped filter, or bilayer lipid membranes indicate that the oscillation can occur even in the absence of the channel protein. The oscillations at artificial membranes are expected to provide fundamental information useful in elucidating the oscillation processes in living membrane systems. Since the oscillations may be attributed to the coupling occurring among interfacial charge transfer, interfacial adsorption, mass transfer, and chemical reactions, the processes are presumed to be simpler than the oscillation in biomembranes. Even in artificial oscillation systems, elementary reactions for the oscillation which have been verified experimentally are very few. 

Similar to molybdenum oxide catalyst the capability to emit singlet oxygen is inherent to Si02 doped by Cr ions as well. Similar to the case of vanadium oxide catalysts in this system the photogeneration occurs due to the triplet-triplet electron excitation transfer from a charge transfer complex to adsorbed oxygen. 

In the context of this chapter, we focus on the undoped or lightly doped 7i-conjugated systems that are commonly referred to as organic semiconductors. Conducting polymers, such as PEDOT PSS, plexcore, polyaniline, polypyrrole, and others are not addressed here as their charge transfer mechanisms are rather different and would warrant an article in its own right. 

In systems in which the charge-transfer excitation band differs from the action spectrum of photoconductivity, the doping effect may be due to a change of recombination path that results in an enhancement of carrier liefetime (e.g. holes in merocyanines and phthalocyanines). (Details on the mechanism are given in 10,11,74).)... 

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