Single-Handed Helical Wrapping of Single-Walled Carbon Nanotubes by Chiral, Ionic, Semiconducting Polymers

Abstract

We establish the requisite design for aryleneethynylene polymers that give rise to single-handed helical wrapping of single-walled carbon nanotubes (SWNTs). Highly charged semiconducting polymers that utilize either an (R)- or (S)-1,1'-bi-2-naphthol component in their respective conjugated backbones manifest HRTEM and AFM images of single-chain-wrapped SWNTs that reveal significant preferences for the anticipated helical wrapping handedness; statistical analysis of these images, however, indicates that ∼20% of the helical structures are formed with the "unexpected" handedness. CD spectroscopic data, coupled with TDDFT-based computational studies that correlate the spectral signatures of semiconducting polymer-wrapped SWNT assemblies with the structural properties of the chiral 1,1'-binaphthyl unit, suggest strongly that two distinct binaphthalene SWNT binding modes, cisoid-facial and cisoid-side, are possible for these polymers, with the latter mode responsible for inversion of helical chirality and the population of polymer-SWNT superstructures that feature the unexpected polymer helical wrapping chirality at the nanotube surface. Analogous aryleneethynylene polymers were synthesized that feature a 2,2'-(1,3-benzyloxy)-bridged (b)-1,1'-bi-2-naphthol unit: this 1,1'-bi-2-naphthol derivative is characterized by a bridging 2,2'-1,3 benzyloxy tether that restricts the torsional angle between the two naphthalene subunits along its C1-C1' chirality axis to larger, oblique angles that facilitate more extensive van der Waals contact of the naphthyl subunits with the nanotube. Similar microscopic, spectroscopic, and computational studies determine that chiral polymers based on conformationally restricted transoid binaphthyl units direct preferential facial binding of the polymer with the SWNT and thereby guarantee helically wrapped polymer-nanotube superstructures of fixed helical chirality. Molecular dynamics simulations provide an integrated picture tying together the global helical superstructure and conformational properties of the binaphthyl units: a robust, persistent helical handedness is preferred for the conformationally restricted transoid binaphthalene polymer. Further examples of similar semiconducting polymer-SWNT superstructures are reported that demonstrate that the combination of single-handed helical wrapping and electronic structural modification of the conjugated polymer motif opens up new opportunities for engineering the electro-optic functionality of nanoscale objects.

Self‐Assembly of Rod‐Coil Block Copolymers on Carbon Nanotubes: A Route toward Diverse Surface Nanostructures

“…In the past decade, there are several reports regarding helical wrapping of single polymers around CNTs. [14] However, because of the size limitation of polymer chains, those helical surface nanostructures are not as obvious as those reported in our present work. The helical wrapping of single polymers is found to enhance properties of or give additional functionality to composites.…”

Assembly and Electronic Applications of Colloidal Nanomaterials

“…[83,151] Similar approaches have been used to flocculate graphene/ethyl cellulose following exfoliation. [163,164] Following sorting, it is necessary to strip the poorly conductive conjugated polymers from the tube walls to improve the charge transport, but their strong affinity for SWCNTs defies effective removal through rinsing at low temperatures. Polyfluorene and polythiophene derivatives or copolymers have been heavily investigated to target specific chiralities of SWCNTs.…”

“…[157,161] In addition, single-handedness SWCNT enantiomers have been separated using conjugated polymers with chiral moieties. [163,164] Following sorting, it is necessary to strip the poorly conductive conjugated polymers from the tube walls to improve the charge transport, but their strong affinity for SWCNTs defies effective removal through rinsing at low temperatures. [165] One method for releasing these polymers is to trigger their conformation change by acids [166] or chelating agents.…”

Emerging enantiomeric resolution materials with homochiral nano-fabrications

“…have been studied in order to obtain near-monochiral suspensions through polymer wrapping. [122][123][124][125] Moreover, recent results demonstrated that this technique allows discrimination between right-and left-handed SWNTs. 126,127 Nakashima and co-workers designed copolymers composed of polyfluorene Reproduced with permission of the American Chemical Society from ref.…”