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

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.