Electrical properties of doped conjugated

Table 2 shows the present state-of-the-art for the electrical conductivity of doped conjugated polymers. The magnitude of the electrical conductivity in polymers is a complex property determined by many stmctural aspects of the system. These include main-chain stmcture and TT-ovedap, molecular... 

Preliminary measurements of electrical conductivity of the conjugated derivatives of PBTAB, PBTB and PTTB obtained by the above treatment with bromine vapor are poor semiconductors with a conductivity of the order 10 °S/cm which apparently is not due to doping. Subsequent electrochemical or chemical doping of these polymers lead to 4-6 orders of magnitude increase in conductivity. Ongoing studies of the electrical properties of these conjugated polymers with alternating aromatic/quinonoid units will be reported elsewhere. 

Metallic properties of doped conjugated polymers are observed in the temperature dependence of conductivity, magnetoresistance, thermopower, magnetic susceptibility, and infrared reflectivity. However, the materials of this class are not yet really metallic with long mean free paths they remain just on the metallic side of disorder-induced M-I transition. This implies that significantly higher electrical conductivities will be obtained with continued improvement of the materials. 

Even if unwanted chemical transformations of doped conjugated materials can be avoided by strict exclusion of air, the long-term stability is limited by a de-mixing of dopant and redox system. An alternative approach to persistent electrical conductors is therefore concerned with the synthesis of intrinsic conductors. Toward that end the lowering of the band gap is desirable which, on the other hand, is known to reduce the chemical stability. The synthetic approaches taken must therefore focus on a compromise between electronically attractive 7i-structure, stability and processability of the material. In conclusion, it is the flexible combination of different areas of research which provides new insights into the properties of monomeric, oligomeric and polymeric radical ions. 

All electronic and electro-optic applications of poly-conjugated systems require the preparation of polymers with high chemical and structural homogeneity. Several optical and electrical properties of conjugated polymers such as their quantum efficiency of electroluminescence or maximum conductivity after doping can be correlated with the concentration of conjugation breaking defects introduced to the polymer upon its preparation. 

One active area of research is completely missing. These are the optical and electrical properties, with effects such as the high conductivity of doped conjugated polymers, electro-luminescence in polymeric light emitting diodes, or the ferro- and piezoelectricity of poly(vinylidene fluoride), to cite only a few examples. There is no good reason for this omission, only that I did not want to overload the book with another topic of different character which, besides, mostly employs concepts which are known from the physics of semi-conductors and low molar mass molecules. 

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