Improving Mobility–Stretchability Properties of Polythiophene Derivatives through Ester-Substituted, Biaxially Extended Conjugated Side Chains

Abstract

P3HT, as one of the most important conjugated polymers, has been reported to possess low mobility and poor stretchability. In this study, two polythiophenes are prepared by attaching ester-substituted, biaxially extended conjugated side chains with backbones of 3-(thiophen-2-yl)-6-(thiophen-3-yl)thieno[3,2-b]thiophene-bithiophene (PDCTT2T) and 3-(thiophen-2-yl)-6-(thiophen-3-yl)thieno[3,2-b]thiophene-difluorobithiophene (PDCTT2T-F) and compared with their respective counterparts without the biaxially extended side chains (thieno[3,2-b]thiophene-bithiophene and thieno[3,2-b]thiophene-difluorobithiophene backbones for PDCTT and PDCTT-F). Through investigating mobility–stretchability properties of these four polymers, the synergetic effect of ester-substituted, biaxially extended conjugation and backbone fluorination is demonstrated to improve mobility–stretchability properties of polythiophenes, especially in a highly stretched state. On the one hand, the biaxially extended side chains implant a more amorphous structure and reinforce the intramolecular charge transfer between polymer backbones. On the other hand, the backbone fluorination confers to a rigidified polymer backbone, facilitating effective intrachain charge transport. As a result, PDCTT2T-F delivers superior mobility (0.20 cm2 V–1 s–1) to PDCTT-F (0.054 cm2 V–1 s–1) alongside 11 times higher mobility retention at a 100% strain. In addition, both PDCTT2T and PDCTT2T-F encouragingly retain decent mobility throughout 800 stretching–releasing cycles (at a 60% strain), outperforming their respective parent polymers without side-chain conjugation that show a one-order decrease in mobility. The results shown in this work signify an effective design strategy to fine-tune mobility–stretchability properties of polythiophenes.

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