JOO ET AL. VOL. 9 ’ NO. 10 ’ 10203–10213 ’ 2015 www.acsnano.org 10203 September 08, 2015 C 2015 American Chemical Society Isolation of Pristine Electronics Grade Semiconducting Carbon Nanotubes by Switching the Rigidity of the Wrapping Polymer Backbone on Demand Yongho Joo, † Gerald J. Brady, † Matthew J. Shea, † M. Bele ´ n Oviedo, ‡ Catherine Kanimozhi, † Samantha K. Schmitt, † Bryan M. Wong, ‡ Michael S. Arnold, † and Padma Gopalan * ,† † Department of Materials Science and Engineering, University of Wisconsin ; Madison, Madison, Wisconsin 53706, United States and ‡ Department of Chemical and Environmental Engineering, and Materials Science and Engineering Program, University of California ; Riverside, Riverside, California 92521, United States S ingle-walled carbon nanotubes (SWCNTs) have exceptional electronic properties that enable a multitude of semiconducting device applications such as field-effect transistors (FETs), 1 photo- voltaics, 2 and gas sensors. 3 To widely use SWCNTs as the semiconducting material in electronic devices, it is essential to sepa- rate the desirable semiconducting SWCNTs from as-synthesized electronically hetero- geneous mixtures of metallic (m-) and semi- conducting (s-) SWCNTs. The challenge of synthetic heterogeneity has motivated the development of a number of sorting tech- niques, including DNA separation, 4 density gradient ultracentrifugation, 5 surfactant as- sisted purification, 6 chromatography, 7 and polymer wrapping. 8 Among these sorting methods, polymer wrapping is considered as one of the most effective methods for selectively isolating large quantities of elec- tronically homogeneous s-SWCNTs. In par- ticular, polyfluorene polymers have been studied as semiconducting-selective agents with selectivity for chirality, diameter and electronic type. 810 Polyfluorenes enable a simple high-fidelity sorting process for milligram-scale quantities of s-SWCNTs to be used in high performance electronic devices and photovoltaic applications. 1113 Developing an understanding for the fac- tors that lead to strong selective interac- tions between the conjugated polymer and the semiconducting tubes is evolving but * Address correspondence to pgopalan@wisc.edu. Received for review June 23, 2015 and accepted September 8, 2015. Published online 10.1021/acsnano.5b03835 ABSTRACT Conjugated polymers are among the most selective carbon nanotube sorting agents discovered and enable the isolation of ultrahigh purity semiconducting singled-walled carbon nanotubes (s-SWCNTs) from heterogeneous mixtures that contain problematic metallic nanotubes. The strong selectivity though highly desirable for sorting, also leads to irreversible adsorption of the polymer on the s-SWCNTs, limiting their electronic and optoelectronic properties. We demonstrate how changes in polymer backbone rigidity can trigger its release from the nanotube surface. To do so, we choose a model polymer, namely poly[(9,9- dioctylfluorenyl-2,7-diyl)-alt-co-(6,60-(2,20-bipyridine))] (PFO-BPy), which provides ultrahigh selectivity for s-SWCNTs, which are useful specifically for FETs, and has the chemical functionality (BPy) to alter the rigidity using mild chemistry. Upon addition of Re(CO) 5 Cl to the solution of PFO-BPy wrapped s-SWCNTs, selective chelation with the BPy unit in the copolymer leads to the unwrapping of PFO-BPy. UVvis, XPS, and Raman spectroscopy studies show that binding of the metal ligand complex to BPy triggers up to 85% removal of the PFO-BPy from arc-discharge s-SWCNTs (diameter = 1.31.7 nm) and up to 72% from CoMoCAT s-SWCNTs (diameter = 0.70.8 nm). Importantly, Raman studies show that the electronic structure of the s-SWCNTs is preserved through this process. The generalizability of this method is demonstrated with two other transition metal salts. Molecular dynamics simulations support our experimental findings that the complexation of BPy with Re(CO) 5 Cl in the PFO-BPy backbone induces a dramatic conformational change that leads to a dynamic unwrapping of the polymer off the nanotube yielding pristine s-SWCNTs. KEYWORDS: conjugated polymers . s- SWCNTs . polymer backbone rigidity ARTICLE