Tuning backbone rigidity and structural regularity in naphthalene diimide-based conjugated polymers for...

Semiconducting single-walled carbon nanotubes (s-SWCNTs) are emerging nanomaterials for next-generation high-performance electronics. However, their application is limited by the co-produced metallic tubes that degrade the device switching performance. Conjugated polymer extraction selectively wraps s-SWCNTs via π-π interactions, yet the effects of the backbone rigidity and structural regularity on sorting behavior remain unclear. Here, a series of donor-acceptor conjugated polymers comprising naphthalene diimide (NDI) acceptors paired with thiophene, bithiophene, and terthiophene donors (T1, T2, and T3), as well as an equimolar random copolymer of thiophene/terthiophene with NDI, T1-3 (a structural isomer of T2), are designed and evaluated as sorting agents. The sorting yield gradually increased from T1 to T3, suggesting that extended conjugation and enhanced backbone rigidity improve polymer-nanotube interactions. T3 exhibits the most stringent diameter selectivity (weighted-average 1.23 nm). All dispersions achieve effective s-SWCNT enrichment, with the purity metric φ decreasing monotonically as the sorting yield increases across the series, reflecting an inherent yield-purity trade-off. T1-3 contains T1-type flexibility and T3-type π-π affinity in a single polymer chain. The two segments act synergistically, endowing T1-3 with the highest sorting yield and the highest hole mobility (2.86 cm² V^-1 s^-1) in field-effect transistor applications, at the cost of the lowest purity among the four polymers. The experimental results indicate that the backbone conjugation length and structural regularity are two important independent design parameters for conjugated polymers in s-SWCNT sorting.