IRAV

The electronic absorption can be attributed to the lowest polaron and/or bipolaron states in the gap (see Figure 3.72). It is clear from the above discussion that some form of transition in the carrier behaviour occurs near c. —0.2 V this is reinforced by a consideration of the IRAV absorptions in Figure 3.83(b). The IRAV bands are reasonably sharp up until —0.2 V after which they broaden and appear less well-defined. 

Clearly there are two sets of absorptions, as shown in Table 3.7, which were attributed to polarons and bipolarons by the authors. All the IRAV bands are relatively narrow and so suggest that the carriers occupy a well-defined number of monomer units. The highest frequency IRAV has been attributed to a combination of the intra-ring OC vibration and the inter-ring C-C stretch which increases in frequency as the conjugation length decreases, consistent with the bipolaron being somewhat shorter than the polaron. 

The initially formed carriers are the polarons, which increase in intensity up to —0.2 V where their intensity attains a constant value independent of any further doping. This can be deduced from the fact that no loss features attributable to polarons can be seen in Figures 3.84(c) or (d). In addition, from c. —0.4 V bipolarons are also generated and it is as a result of the growing-in of these absorptions that the IRAV bands appear to broaden out but they only become important at potentials > —0.2 V. 

Dinitroanisole has been made only by this method.1 1 Lobry de Bruyn, Rec. Irav. chim. 9, 208 (1890). 

Observation of the charged carrier is even more favourable in the IR regime (photoinduced IRAV studies). In semiconducting, conjugated polymers, the quasi-one-dimensional electronic structure has to be strongly coupled to the chemical (geometrical) structure. As a result, nonlinear excitations (solitons, polarons and polaron pairs) are dressed with local structural... 

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