Conductivity in Organic Systems

FIGURE 18.3 Polarization around a negatively charged molecule in the crystal. 

Although the work of Akamata et al. did not involve photoexcitations, it may be of interest to lock at the spectrum. The energy of the itit transitions is generally 

FIGURE 18.4 A perylene molecule (a). The molecule on (b) is perylene diimide (PDI). The -NH group may be exchanged by other groups to obtain novel pigments with other hues and colors. 

The absorption spectrum of perylene is roughly the same as for molecules where substitutions have been made in the perylene molecule. As usual in planar systems, the polarization (transition moment) is in the xy-plane. The snbstituents are not directly involved in the transition and only slightly modify the energy of the transitions. This is enough to obtain pastel pigments with different hnes. 

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Extensive ir-conjugation is also often associated with enhanced conductivity in organic systems (6). Polyacetylene and polythiophene which in the doped state exhibit very high electrical conductivity also exhibit relative large third-order nonlinear optical effects in... 

However, metallic conduction in organic systems had been dreamt of as early as 1911 [1]. Until the mid 1960s the serious researchers of the organic solid state were few Hideo Akamatsu [2], Noel S. Bayliss [3], Melvin Calvin [4], Daniel D. Eley [5], Helmuth Kainer [6], Aleksandr I. Kitaigorodskii [7], Jan Kommandeur [8], Yoshio Matsunaga [9], Harden M. McConnell [10], Albert Szentgyorgyi [11], A.N. Terenin [12] and A.T. Vartanyan [12]. 

Conductivity in organic systems is broadly divided into conductivity in crystals or films and conductivity in polymers. Single crystals without impurities are well suited for investigating the intrinsic charge transport properties of organic semiconductors. 

The role of reversed micelles in the manufacture of fine chemicals with enzymes also needs to be assessed and analysed. An outstanding example is lipase catalysed interesterification to produce cocoa butter substitute from readily available cheap materials (Luisi, 1985). This example of reversed micelles is sometimes referred to as a colloidal solution of water in organic systems. A number of water insoluble alkaloids, prostanoids, and steroids have been subjected to useful transformations (Martinek et al., 1987). Peptide synthesis has also been conducted. The advantages of two liquid phases are retained to a very great extent the amount of water can be manipulated to gain advantages from an equilibrium viewpoint. 

The discovery of metallic conductivity in organic solids stands as a major scientific discovery of the twentieth century <1995S215>. From a total of several organic 7t-donors described in the literature, five (438a-c, 439, and 440) are four-heteroatom bicyclic 5 6 systems with two heteroatoms in each moiety. 

Evaluations of an integrated adsorption system were also conducted. In this system, by varying the pH conditions, the dissolved organics (model compounds) are separated into fractions by isolation onto Amberlite XAD-8, AG MP-50 cation-exchange resin, and graphitized carbon black. The procedure is based on the separation of organic solutes into hydrophobic and hydrophilic neutral, acidic, and basic fractions. 

When a substance exhibits an appreciable electron conduction, this is an indication that there are numerous free levels at various small distances from the occupied states. Light of all wave lengths will, therefore, be strongly absorbed the substance is almost completely opaque and reflects nearly all light in the massive state. In the finely divided state the substance is black. Conversely, it can be said that black substances, at any rate when they do not consist of separate molecules such as the organic colouring matters, are also electron conductors (many metallic oxides and sulphides). In dyes (see p. 253) one could speak of an intramolecular conduction in the system of the re electrons of the conjugated double bonds. 

Effective molarities of intramolecular reactions, 17, 183 Electrical conduction in organic solids, 16, 159 Electrochemical methods, study of reactive intermediates by, 19, 131 Electrochemistry, organic, structure and mechanism in, 12, 1 Electrode processes, physical parameters for the control of, 10, 155 Electron spin resonance, identification of organic free radicals by, 1, 284 Electron spin resonance studies of short-lived organic radicals, 5, 23 Electron-transfer reaction, free radical chain processes in aliphatic systems involving an, 23, 271... 

An efficient solution for the subtraction method was proposed by Bassette and Whit-nah [16]. The reactions were conducted in a system containing two phases water and carbon tetrachloride. The test mixture, which consisted of an aqueous solution of organic compounds, was used as one of the two phases (aqueous). After shaking and separation of the layers, the carbon tetrachloride was analysed with the extracted compounds by GC (see Fig. 5.3A). 

These compounds have a residual conductivity Oi 35k> 10000 Q cm [98]. According to the treatment reported in refs [117], [3], the superconductivity in organic systems requires a minimum residual conductivity of 6000 Q an, a value consistent with the theoretical estimation based on the Anderson localization. Con unds (13) and (14) could be candidates for superconductivity as they fulfill... 

The solid polymer eleetrolytes are mixtures of an inorganic salt and an organic polymer, preferably polyether like poly(ethylene oxide) (PEO). Relaxation and diffusion phenomena in context of ionic conductivity in those systems are our concern in this paragraph. 

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