Enhanced mobility preservation of polythiophenes in stretched states utilizing thienyl-ester conjugated side chain

Recently, diverse approaches to synthesizing intrinsically stretchable conjugated polymers have been presented, such as incorporating the conjugation break spacers or intermolecular interactions in conjugated backbones, resulting in a compromise in the charge carrier mobility. In this study, polythiophenes with flexible [2,2':5′,2'':5″,2‴]-quaterthiophene (QT) or rigid 2-([2,2′-bithiophen]-5-yl)thieno[3,2-b]thiophene (BTTT) backbones were engineered with ester- (E−), thienyl- (T-), and thienyl-ester-substituted (TE) side chains for an enriched amorphous content and an improved mechanical tolerance. Polythiophene with QT backbone and TE side chain (PQT-TE) represents the best mobility−stretchability properties evidenced by the polarized UV–vis absorption, grazing incidence X-ray diffraction, and surface morphological analyses. Accordingly, PQT-TE presents a higher chain conformability and crack-onset strain than QT-based polythiophene with T (PQT-T) or E (PDCBT) side chains. This improvement originated from enriched amorphous domains and enhanced backbone planarity using a biaxially extended conjugation design. PQT-TE exhibits high orthogonal mobility preservations of (64, 90)% under 60% strain parallel/perpendicular to the channel direction. Notably, PQT-TE achieves high orthogonal mobility preservations of (48, 65)% after 800 cyclic stretch−release tests under 60% strain, and these improvements are similarly observed in that of BTTT-based polythiophene (PBTTT-TE). This study demonstrates that the jointed design of the biaxial extension and ester functional groups is efficacious in improving the mobility−stretchability properties of polythiophenes.