Polythiophenes molecular order

S.J., Chang, T.Y., Chang, C.W., Joo, M.K., Ryu, C.Y. and Cho, K.W., Enhancement of field-effect mobility due to surface-mediated molecular ordering in regioregular polythiophene thin film transistors, Adv. Func. Mater, 15, 77-82, 2005. 

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. 

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

Molecular self-organization in solution depends critically on molecular structural features and on concentration. Molecular self-organization or aggregation in solution occurs at the critical saturation concentration when the solvency of the medium is reduced. This can be achieved by solvent evaporation, reduced temperature, addition of a nonsolvent, or a combination of all these factors. Solvato-chromism and thermochromism of conjugated polymers such as regioregular polythiophenes are two illustrative examples, respectively, of solubility and temperature effects [43-45]. It should therefore be possible to use these solution phenomena to pre-establish desirable molecular organization in the semiconductor materials before deposition. Our studies of the molecular self-assembly behavior of PQT-12, which leads to the preparation of structurally ordered semiconductor nanopartides [46], will be described. These PQT-12 nanopartides have consistently provided excellent FETcharacteristics for solution-processed OTFTs, irrespective of deposition methods. 

The coupling of the electronic structure of the conjugated polythiophene to the conformation can account for chromic phenomena as well as for aspects of electronic transport of the materials in their undoped or doped states. The order-disorder transition of the polymer chains, between a planar and a non-planar state, is governed by molecular mechanisms related to the nature and regularity of side-chain substituents. 

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