High-Efficiency Quantum Defect Engineering in Carbon Nanotubes via Oxygen-Free Photochemistry

Single-walled carbon nanotubes (SWCNTs) offer potential for a wide range of applications from optoelectronic devices to biomedical diagnostics. One reason are their tunable optical properties, which can be further tailored by introducing a small number of quantum defects. However, the chemical conditions to obtain an optimal number and specific type of quantum defect is difficult to control. Here, we demonstrate that oxygen-free conditions are crucial to control the spectral features. To this end, we analyze the photochemical reaction of (6,5)-SWCNTs with different alkyl and aryl halides, as well as alkenyl/alkynyl compounds under UV irradiation. Removal of oxygen or addition of sulfites shifts the quantum defect related E11* emission peak from ~ 1130 nm to ~ 1100 nm, which suggests that different types of quantum defects are formed. For aryl halides, these conditions increase the E11*/E11 ratio up to 90 %, while reducing the required reactant concentration by ~ 90 %, with reaction times < 10 minutes. For the less reactive alkyl halides, ~ 80-fold smaller reactant concentrations achieve the same E11*/E11 ratios compared to oxygen containing conditions. This procedure allows us to investigate the combined effect of quantum defects and DNA functionalization of SWCNTs on the detection of small molecules. It underlines that efficient incorporation of quantum defects opens a new chemical dimension for SWCNT chemistry and photophysics.