Abstract
This paper describes the effectiveness of donor–acceptor (D-A) conjugated polymers to disperse and select for semiconducting single-walled carbon nanotubes (s-SWCNTs) when enhanced by the inclusion of polar oligoethylene glycol-based side chains, without altering the D–A backbone. We designed and synthesized two sets of naphthalenediimide(NDI)-alt-bithiophene(T2)-based conjugated polymers with one of two alkyl side chains (decyl and dodecyl chains) of different lengths and with or without polar triethylene glycol side chains. The resulting low-band-gap copolymers all effectively disperse and select for s-SWCNT, but the inclusion of polar side chains enhances the interactions between the polymer backbone and the walls of the s-SWCNTs relative to the polymers with only alkyl side chains. As a result, the wrapping and selection efficiency of the polymer-SWCNT systems with polar side chains are both significantly enhanced. We further optimized the binding energy and surface coverage by combining glycol ether and dodecyl side chains to maximize wrapping efficiency, leading to a field-effect mobility of 2.82 cm2 V–1 s–1 and on/off current ratios of ∼2 × 107 in polymer-wrapped SWCNTs. Our results provide insight into the role of the side-chain interactions in the polymer wrapping and dispersion technique, and, because we focus on manipulating side chains, they can be generalized for other conjugated polymer backbones.
Highlights
Ultrapure semiconducting single-walled carbon nanotubes (s-SWCNT) are highly desired in electronics as nanometer building blocks and have drawn considerable attention due to their superior semiconducting properties.[1−14] the techniques for SWCNT synthesis, including arc-discharge,[15,16] laser ablation,[17−19] and chemical vapor deposition (CVD),[20−23] inevitably introduce metallic single-walled carbon nanotubes (m-SWCNT) in the product
We demonstrate that the effectiveness of D−A conjugated polymers to disperse and select s-SWCNTs can be significantly improved by including polar triethylene glycol (TEG)-based side chains, without any alteration to the D−A backbone
Series polymers PNDIUnd-AT-C10, PNDITEG-AT-C10, and PNDITEG-AT-C12 and −5.37, −5.61, and −5.65 eV for NDIAH series polymers PNDIUnd-AH-C10, PNDITEG-AH-C10, and PNDITEG-AH-C12. These results reveal that the incorporation of the TEG side chain into the polymers can stabilize the lowest unoccupied molecular orbitals (LUMOs) level, indicating that a polar TEG side chain has an inductive effect on the electronic structure and pushes down the energy levels.[54]
Summary
SWCNT) are highly desired in electronics as nanometer building blocks and have drawn considerable attention due to their superior semiconducting properties.[1−14] the techniques for SWCNT synthesis, including arc-discharge,[15,16] laser ablation,[17−19] and chemical vapor deposition (CVD),[20−23] inevitably introduce metallic single-walled carbon nanotubes (m-SWCNT) in the product. We hypothesize that a D−A conjugated polymer decorated with highly polar side chains should interact strongly with SWCNTs, increasing the selectivity for s-SWCNTs compared to polymers with nonpolar side chains In this contribution, we demonstrate that the effectiveness of D−A conjugated polymers to disperse and select s-SWCNTs can be significantly improved by including polar triethylene glycol (TEG)-based side chains, without any alteration to the D−A backbone. We demonstrate that the effectiveness of D−A conjugated polymers to disperse and select s-SWCNTs can be significantly improved by including polar triethylene glycol (TEG)-based side chains, without any alteration to the D−A backbone To this end, we designed two series of naphthalenediimide-alt-bithiophene-based conjugated copolymers; one series of copolymers (NDI-AT series) is derived from a naphthalenediimide monomer and tail-to-tail bithiophene monomer, and another (NDI-AH series) is derived from a naphthalenediimide monomer and a head-to-head bithiophene monomer. This work clearly demonstrates the critical role of the side chain during polymer design and contributes to a deeper understanding of the relationship between the polymer structure and the ability of the polymer for dispersing and selecting sSWCNTs
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