N-type semiconducting polymers with an improved isotropic mobility–stretchability stability by using structural isomers as conjugation break spacers

Abstract

The structural isomeric effect on the conjugation-break spacers (CBSs) design in stretchable conjugated polymers hasn't been investigated. In addition, achieving isotropic mobility–stretchability performance is challenging, as crack formation and polymer chain alignment can make the mobility anisotropic. In this study, three alicyclic CBSs were incorporated into the backbone of naphthalenediimide (NDI)-based n-type semiconducting polymers to enhance their mechanical and electronic performance. Of the three CBSs, 2,5-tricyclodecanedimethanol (TCD–CBS) and an isomeric mixture of tricyclodecanedimethanol (rTCDs–CBS) feature tricyclic structures derived from dicyclopentadiene, whereas trans-1,4-cyclohexanediol (tCH–CBS) incorporates a monocyclic structure. The experimental results demonstrate that the structural configuration of the CBS units has a significant influence on polymer aggregation, crystallinity, chain alignment, and mechanical stability. TCD, with its rigid tricyclic structure of TCD–CBS that promotes predominant face-on stacking, delivers high initial mobility but lacks mechanical durability under strain. In contrast, tCH features a flexible monocyclic structure of tCH–CBS that favors edge-on stacking, enables isotropic transport, but suffers from low mobility and poor structural stability due to its high chain conformability under deformation. However, unlike TCD and tCH, rTCDs comprising rTCDs–CBS offers balanced performance by introducing moderate structural disorder that supports a bimodal molecular orientation. This configuration increases free volume and creates additional charge carrier pathways, allowing the polymer to maintain ductility and stable charge transport under strain. After 1000 cycles at 40% strain, rTCDs retained 77% of their mobility in the parallel direction and 104% in the perpendicular direction, relative to single-cycle performance. These results highlight the potential of isomeric design in CBS units to achieve both mechanical flexibility and isotropic electronic performance in stretchable semiconducting polymers for wearable and deformable electronics.