Decoration of Polyfluorene-Wrapped Carbon Nanotubes via Strain-Promoted Azide–Alkyne Cycloaddition

Abstract

Developing methodologies that can efficiently decorate carbon nanotube surfaces with various molecular structures while avoiding damage to nanotube optoelectronic properties is an ongoing challenge. Here, we outline a methodology to perform chemistry on the nanotube surface without perturbing optoelectronic properties. Reactive, noncovalently functionalized polymer–nanotube complexes were prepared using polyfluorene with azide groups in its side chains. The azides enable strain-promoted azide–alkyne cycloaddition to occur between polymer–nanotube complexes and small molecules or polymers derivatized with a strained cyclooctyne. This reaction was found to occur efficiently at room temperature, without any catalyst or byproduct removal required. The reaction was monitored by infrared spectroscopy via the disappearance of the polymer azide stretch at ∼2090 cm–1, and this chemistry resulted in no damage to the nanotube sidewall, as evidenced by Raman spectroscopy. The azide-containing polyfluorene was used to prepare an enriched dispersion of semiconducting carbon nanotubes in organic media, which could then be redispersed in aqueous solution post-click with strained cyclooctyne-functionalized poly­(ethylene glycol). Taking advantage of the ability to preserve optoelectronic properties, solvatochromism of an identical subset of semiconducting carbon nanotubes was investigated using absorption, fluorescence, and Raman spectroscopy. It was found that, in aqueous media, fluorescence was nonuniformly quenched among the different semiconducting species and that there was a significant red-shift in the emission of all nanotubes in D2O relative to nonpolar toluene.

Preparation of stimulus‐responsive, polyfluorene‐wrapped carbon nanotubes via palladium cross coupling

“…To prepare reactive polymer–SWNT complexes, we first synthesized an aryl iodide‐containing polyfluorene ( PF‐PhI ). The precursor polyfluorene with alkyl bromides in the side chain ( PF‐Br ) was prepared according to literature procedures . Gel permeation chromatography analysis showed that PF‐Br had an M n of 100 kDa, corresponding to a degree of polymerization of ~101, and a dispersity (Đ) of 3.9.…”

“…We have recently been investigating a simple way to simultaneously decorate single‐walled carbon nanotubes (SWNTs) while avoiding SWNT damage . Since their discovery in 1991, efforts have been made to exploit the extraordinary mechanical, structural, and optoelectronic properties of SWNTs.…”

“…In our group, we have incorporated azide groups in the conjugated polymer side chains, such that upon complexation with SWNT surfaces, a latently reactive polymer–SWNT complex is produced. This strategy has allowed for the decoration of carbon nanotube surfaces using copper‐catalyzed or strain‐promoted azide–alkyne cycloaddition. In the present work, we sought to expand on the available chemical toolbox applicable to this methodology by utilizing Pd‐catalyzed cross coupling to prepare stimulus‐responsive SWNT complexes.…”

Light‐driven atom transfer radical polymerization on supramolecular complexes of conjugated polymers and single‐walled carbon nanotubes

“…Our group has been investigating the decoration of single‐walled carbon nanotubes (SWNTs) with conjugated polymers to impart reactivity to the polymer–nanotube complex . This strategy operates by incorporating functional groups into the conjugated polymer side chains to perform chemistry on the adsorbed conjugated polymer, which avoids damage to the SWNT structure.…”

“…This strategy operates by incorporating functional groups into the conjugated polymer side chains to perform chemistry on the adsorbed conjugated polymer, which avoids damage to the SWNT structure. By incorporating azide groups into the conjugated polymer side chains, copper‐catalyzed or strain‐promoted azide–alkyne cycloaddition (CuAAC) can be used to decorate the SWNT surface. We have also incorporated aromatic iodides to enable Pd cross‐coupling to the polymer–SWNT conjugate, and have prepared water‐dispersible polymer–SWNT complexes for aqueous click functionalization .…”