Handle-free attachment of small molecules on single-walled carbon nanotubes

Few chemical methods controllably generate sp3 defects on single-walled carbon nanotubes, and fewer still create quantum wells that localize excitons and enhance near-infrared emission. Here we describe an aqueous, nanotube-catalysed Fenton reaction that enables the conjugation of an extensive range of small molecules lacking traditional single-walled carbon nanotube conjugation handles, generating quantum well defects with tunable electro-optical properties. We demonstrate the attachment of over 150 unique small molecules, including alcohols, amines, carbonyls, acrylates, amino acids and peptides. The resulting optical properties are governed by the electronic structure of the attached group, which determines the relative configuration of defects (ortho or para) within the graphitic lattice. Time-dependent density functional theory calculations confirm the assignment of the observed emission peaks to specific defect configurations. These molecularly driven effects enable precise control over the optical properties of the nanotubes, broadening the design space of rationally engineered quantum well-bearing nanomaterials. Aqueous nanotube-catalysed Fenton chemistry enables handle-free attachment of chemically diverse small molecules to single-walled carbon nanotubes, generating tunable sp3 quantum-well defects and redshifted near-infrared emission. The identity of the conjugated group determines defect configurations and emission wavelength, providing a scalable strategy for the rational design of nanotube-based photonic materials.