Mobility, charge carrier chart

Several related polymers prepared via chemical polymerization are mentioned here as they are closely related to the systems discussed above. Polymers 69 and 70 (Chart 5.20) have been prepared via Pd-catalyzed Stille coupling [77]. The electrochemistry of these polymers both in solution and as thin films shows well-defined redox waves due to the metal and oligothiophene units. ESR reveals the presence of mobile charge carriers in the polymer and a polaronic band in the UV-Vis spectrum of the doped material correlates with the ESR results [78]. Photophysical analysis of the polymers reveals that in the case of the Ru polymers the k state is lower in energy than the MLCT band. 

Huisman et al. studied the LC behavior of semiconducting oligothiophenes 2.53 (n = 4-8) (Chart 1.12), which were substituted by polymerizable acrylate groups [119]. By using these materials for the fabrication of OFETs, it was observed that the use of polymer films resulted in a decrease in mobility by a factor of 10 compared with transistors made from the bisacrylate monomer. For example, the charge carrier mobility of 2.53 (n = 6) after polymerization was 6 x 10 " cm V s compared with 4 x 10 cm V s before... 

The attachment of hexyl-capped quaterthiophenes to a carbosilane core via longer alkyl side-chains was achieved by hydrosilylation reactions. JCirchmeyer et al. obtained quaterthiophene-fiinctionalized tetrahedral structure 5.51 (Chart 1.73), which were highly soluble in organic solvents. In OFETs these solution-processable materials showed excellent charge carrier mobility values of 10 cm V s and on/off-ratios of 10 . Because of the high proportion of saturated parts in the core, this result is... 

There may be contributions to the conductivity from several different types of carrier, notably electrons and holes (a hole is an electron vacancy carrying an equivalent positive charge) in electronic conductors, and cation and anion pairs in ionic conductors. Theories of conduction aim to explain how n and fj. are determined by molecular structure and how they depend on such factors as temperature and applied field. In addition, in polymers the mobility will be affected by the sample morphology. Just as a large range of conductivity is observed for different materials so there is a large range of mobility values. Data for a selection of systems are displayed on the mobility chart (Fig. 4.2). 

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