Reactive, Aqueous-Dispersible Polyfluorene-Wrapped Carbon Nanotubes Modulated with an Acidochromic Switch via Azide–Alkyne Cycloaddition

Decorating hydrophobic carbon nanotube surfaces efficiently in aqueous solution without adversely affecting nanotube optoelectronic properties remains a challenge. In this work, we designed a water-soluble polyfluorene derivative that contains azide groups and polyethylene glycol grafts in the side chains. This polyfluorene derivative was used to coat carbon nanotube surfaces, producing a latently reactive and aqueous-dispersible polymer–nanotube complex. Reaction progress of the aqueous polymer–nanotube dispersion with various polar and nonpolar alkyne derivatives was followed using infrared spectroscopy. Decoration of the polymer–nanotube complex with various small molecules or polymers was found to modulate the surface properties of the resulting nanohybrid thin films. Additionally, we developed a vanillin-derived indolinooxazolidine switch that is functionalized with a terminal alkyne and appended it to the polymer–nanotube complex. This switch possesses two long-lived states that are interchangeable via exposure to acidic or basic conditions. We studied the fluorescence emission response of the polymer–nanotube complex using UV–vis–NIR and fluorescence spectroscopy. The acidochromic switch linked to the polymer–nanotube complex enables control over nanotube emission, while the free switch in solution does not. Photoluminescence mapping reveals a nanotube species-dependent fluorescence quenching response to charge buildup at the nanotube surface.