"The Oligomer Approach Towards Understanding Crystallization of Polyalkylthiophene Semiconductors"

It is well acknowledged that carrier mobilities of conjugated polymers can be further enhanced by highly crystalline arrangement of alkyl side chains and backbones. However, to date, a detailed description and mechanism of polymer semiconductor crystallization is still not reported in literature due to the scarcity of polymer crystals. Thiophene oligomers are excellent model structures for the corresponding polydisperse polymers to elucidate the structure-property relationship. 

The objective of this study is to develop a deeper and more fundamental understanding of the chain packing in low molecular weight polymer in crystalline thin films and its role in the resulting electronic properties of the material. For this purpose we have synthesized a special homologue series of oligomers of a benchmark building block, didodecylquaterthiophene, ranging in length from the monomer to the hexamer. Crystalline thin films of these materials are be prepared by various solution-casting techniques, and then characterized by a combination of synchrotron grazing incidence X-ray scattering (GIXS) including crystallographic refinement calculations, transmission electron microscopy (TEM), and electrical measurements in thin film devices, such as organic field effect transistors. An improved understanding of the molecular packing of these oligomers in thin films will help us to understand and ultimately control crystallization in higher molecular weight polymers, as the oligomers will serve as crystallization models. The results from this work will have a high impact on the general synthetic design rules for semiconducting polymers with controlled molecular weight and narrow polydispersity that produce highly crystalline thin films.