Controlling conjugated polymer morphology by precise oxygen position in single-ether side chains
Pablo Durand, Huiyan Zeng, Badr Jismy, Olivier Boyron, Benoît Heinrich, Ioannis Moutsios, Dimitri A. Ivanov, Laurent Herrmann, Olivier Bardagot, Alina V. Mariasevskaia, Alexey P. Melnikov, Martin Brinkmann, and Nicolas Leclerc
The development of semiconducting polymers with polar side chains is gaining considerable momentum, driven by thermoelectric, storage and bioelectronic applications. To date, most molecular designs are focusing on oligo(ethylene glycol) (OEG) side chains, containing multiple oxygen atoms. While OEG side chains effectively promote dopant/ion uptake, they also suffer from a low crystallinity, which limits the ordering of the polymer and hence its charge transport properties. Recently, single-ether side chains, containing a single oxygen atom, have emerged as an alternative. They offer a compromise between polarity, to promote doping, and self-assembly order, to promote transport properties. In this work, we provide a full understanding of the impact of the position of the oxygen atom along the side chain on the morphological and transport properties of novel high-performance PBTTT polymers. By using nanocalorimetric measurements coupled with X-ray scattering, we show that single-ether side chains are crystalline and, more importantly, that the degree of morphological order of the polymers can be controlled by varying the position of the oxygen atom (crystallinity index). This work showcases a new design tool to guide chemists in the development of high-performance doped semiconductors and organic mixed ionic- electronic conductors with optimal balance between polymer polarity and molecular order.
