Molecular solid-state conductivity

To control the [2 + 2] photoreaction such that it is possible to conduct molecular solid-state synthecir by design, recent efforts were directed toward the application of supramolecular chemistry.Specifically, the field of... 

Following the general trend of looldng for a molecular description of the properties of matter, self-diffusion in liquids has become a key quantity for interpretation and modeling of transport in liquids [5]. Self-diffusion coefficients can be combined with other data, such as viscosities, electrical conductivities, densities, etc., in order to evaluate and improve solvodynamic models such as the Stokes-Einstein type [6-9]. From temperature-dependent measurements, activation energies can be calculated by the Arrhenius or the Vogel-Tamman-Fulcher equation (VTF), in order to evaluate models that treat the diffusion process similarly to diffusion in the solid state with jump or hole models [1, 2, 7]. 

Conjugated polymers are generally poor conductors unless they have been doped (oxidized or reduced) to generate mobile charge carriers. This can be explained by the schematic band diagrams shown in Fig. I.23 Polymerization causes the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the monomer to split into n and n bands. In solid-state terminology these are the valence and conduction bands, respectively. In the neutral forms shown in Structures 1-4, the valence band is filled, the conduction band is empty, and the band gap (Eg) is typically 2-3 eV.24 There is therefore little intrinsic conductivity. 

Fig. 7. Solid state molecular transistor based on polyaniline bridged microelectrodes. PVA layer of polyvinyl alcohol 1 drain current Vg gate voltage rendering the polyaniline non-conductive Vg gate voltage switching on conductivity of the polyaniline layer (from ref.

The bridging polymer is a conducting poly(3-methyIthiophene) or polyaniline and the solid state redox conduction between all electrodes is accomplished by a common coating with poly(ethyleneoxide)/Li" CF3S03- or poly(vinyl alcohol)/ The polyaniline based molecular transistor proved as a very sensitive moisture detector it works well in a dry argon atmosphere but in water saturated argon the device cuts out... 

The SCF method for molecules has been extended into the Crystal Orbital (CO) method for systems with ID- or 3D- translational periodicityiMi). The CO method is in fact the band theory method of solid state theory applied in the spirit of molecular orbital methods. It is used to obtain the band structure as a means to explain the conductivity in these materials, and we have done so in our study of polyacetylene. There are however some difficulties associated with the use of the CO method to describe impurities or defects in polymers. The periodicity assumed in the CO formalism implies that impurities have the same periodicity. Thus the unit cell on which the translational periodicity is applied must be chosen carefully in such a way that the repeating impurities do not interact. In general this requirement implies that the unit cell be very large, a feature which results in extremely demanding computations and thus hinders the use of the CO method for the study of impurities. 

Unlike solid state -stacks, however, double helical DNA is a molecular structure. Here CT processes are considered in terms of electron or hole transfer and transport, rather than in terms of material conductivity. Moreover, the 7r-stack of DNA is constructed of four distinct bases and is therefore heterogeneous and generally non-periodic. This establishes differences in redox energetics and electronic coupling along the w-stack. The intimate association of DNA with the water and counterions of its environment further defines its structure and contributes to inhomogeneity along the mole-... 

Perhaps the common characteristic of all contributions to this volume is the permanent concern about the intimate relationships between the structural and electronic properties. Indeed, the careful design of increasingly complex molecular and supramolecular architectures allows us now to anticipate many molecular and solid state properties, but the final solid state structures are always the results of many competing interactions. The resulting electronic properties of these radical assemblies, whether conductivity or magnetism, are always very sensitive to minute modifications of their solid state structures and one of the main difficulties through... 

Phthalocyanine-based molecular metals and conductive polymers have been prepared and investigated by 13C solid state NMR. Among others, Ge serves as a central atom219,220. However, no discussion of a special role of the metal is presented in this work. 

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