Polythiophenes solid state conformation

The reversible thermochromic effect observed here and in the solid state is associated with enhanced order of the alkyl side chains with decreasing temperature, facilitating coplanar conformers in the polythiophene backbones, with the attendant enhancement in the 7t-7t -transition of the thiophene ring electronic absorption spectra and improvement in electronic conduction of the doped film. 

On the basis of all these results, striking chromic effects can be triggered by a variety of external stimuli, including heat, pressure, electromagnetic radiation, ions, molecules, etc. In some polythiophene derivatives, these field-induced conformational transitions do not only alter the optical features of the materials of interest but their electrochemical characteristics as well, giving rise to the possible development of various devices in different areas, such as in sensing, detection and recognition of numerous chemical and biochemical moieties or solid-state devices. 

The solution studies indicate that the ordered supramolecular disk structures with globally ordered extended conformations of polythiophene are desirable precursors to self-assembled PAT films, whereas the needle-like structures do not pack well and cannot give a globally ordered structure. This discovery implicitly has a profound effect on film casting and the resultant solid-state order (discussed below). The light-scattering data also suggest that solution spectra will vary with temperature, concentration, solvent composition, and the thermal history of the sample. 

In Table 9.5, the physical properties of these random, HT poly(3-alkylthiophene) copolymers are given. It can seen that copolymer 17 exhibits a solution Amax of 510 nm, which corresponds to one of the longest conjugation lengths known for a polythiophene in solution. It can also be seen that there is little difference in the absorption maximum between solution and the solid state (25 nm). Apparently 17 has an extended planar conformation even in solution, owing to the lack of steric hindrance caused by alkyl side chains and solution supra-molecular ordering. 

On the basis of all these results, a striking parallelism seems to exist between the chromic phenomena observed in polythiophenes, polydiacetylenes, and polysilanes. It is even possible that the same driving force could explain most of the optical features observed in these conjugated materials. As reported in the previous sections, these chromic phenomena could be described in terms of a planar-nonplanar conformational transition of the main conjugated backbone. However, it is unclear whether this conformational transition is related to an intrachain or interchain mechanism. Results obtained in the solid state are not particularly useful in attempts to... 

Crystallinity, molecular order, conformation in solid state Morphology and Density Properties of polythiophenes Conductivity... 

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