Versatile Photofunctionalization of Carbon Nanotubes via [4 + 2] Cycloaddition: A Facile Route to Hybrid Nanomaterials

The [4 + 2] photofunctionalization of carbon nanotubes of different characteristics, such as single-walled carbon nanotubes (0.9 and 1.4 nm diameter) or multiwalled carbon nanotubes (10 nm diameter), with aryl cyclobutyl amines <b>3</b> of diverse nature in the presence of common organic photocatalysts is presented. Through a facile synthetic protocol, a series of modified amines <b>3</b> is prepared, which undergo a photocatalyzed oxidative ring opening to subsequently react with the nanotube wall. Under the best reaction conditions (Rhodamine B, white light-emitting diode, 40 h), an 8-20% functionalization degree in the form of <i>N</i>-cyclohexylamine moieties is achieved. The reaction is general with respect to the type of nanotube employed, the electronic characteristics of the amine (decorated with electron-donating and electron-withdrawing groups), and it is homogeneous throughout the whole nanotube particle without affecting the morphology of the samples, as demonstrated by the characterization techniques performed. In addition, the method allows for postfunctionalization treatments by the on-surface hydrolysis of an ester-modified aryl cyclobutyl amine and subsequent amidation with amino-decorated organic polymer nanoparticles. Thus, a hybrid material with different properties compared to the simple composite is obtained using this photochemical carbon nanotubes functionalization.