Solid-state properties, conjugated polymer

The electrical conductivity of a material is a macroscopic solid-state property since even in high molecular-weight polymers there is not just one conjugated chain which spans the distance between two electrodes. Then it is not valid to describe the conductivity by the electronic structure of a single chain only, because intra- and interchain charge transport are important. As with crystalline materials, some basic features of the microscopic charge-transport mechanism can be inferred from conductivity measurements [83]. The specific conductivity a can be measured as the resistance R of a piece of material with length d and cross section F within a closed electrical circuit,... 

After covering the interplay of the excited state with chemical and structural defects, we will now consider how changes in the chemical structure affect the properties of conjugated polymers, in particular the focus will be put on PPP-type structures with increasing degree of bridging. In the following, the most important issues related to both the chemical structure and the solid state properties... 

The relation between the EA response and the macroscopic nonlinear properties of the material has been drawn by a classical approach. In Section 19.3.3, the mechanism behind the field-induced variation will be explored by a quantum mechanical approach. In molecular solids and in conjugated polymers, where the states are localized to a high degree, the change in a with the electric field is in general ascribed to a Stark shift of the molecular energy levels. 

The transfer of PCSs from solutions into the solid state may be accompanied by the origination of hydrogen and salt bonds, by associations in crystalline regions, or by charge transfer states and some other phenomena. These effects are followed by some conformational transformations in the macromolecules. The solution of the problem of the influence of these phenomena on the conjugation efficiency and on the complex of properties of the polymer is of fundamental importance. 

An important challenge in the design of novel conjugated polymers is the synthesis of materials with tailor-made solid-state electronic properties. This section outlines the synthesis of the most significant classes of poly(para-phenylenevinylene)s (PPVs), poly(para-phenylene)s (PPPs), and related structures. Furthermore, this review demonstrates that the chromophoric and electronic properties of conjugated rr-systems are sensitive to their molecular and supra-molecular architecture. 

An important difference between luminescent conjugated polymers and laser dyes is that the former still exhibit strong optical gain in the solid state. This property means that luminescent conjugated polymers can be used to produce stimulated emission in thin films of these materials. 

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