Polar Side Chains Enhance Selection of Semiconducting Single-Walled Carbon Nanotubes by Polymer Wrapping
Gang Ye, Wytse Talsma, Karolina Tran, Yuru Liu, S. Gerhard Dijkstra, Jiamin Cao, Jianhua Chen, Junle Qu, Jun Song, Maria Antonietta Loi, Ryan C. Chiechi
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 cm<sup>2</sup> V<sup>-1</sup> s<sup>-1</sup> and on/off current ratios of ∼2 × 10<sup>7</sup> 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.