Bright Near-Infrared Emission from Luminescent Defects in Semiconducting Single-Walled Carbon Nanotubes

The controlled functionalization of chirality-sorted semiconducting single-walled carbon nanotubes (SWCNTs) with luminescent sp³ or oxygen defects increases their photoluminescence quantum yield in the near-infrared (1000 – 1500 nm) and enables their application in optoelectronic devices (Adv. Opt. Mater. 2023, 11, 2300236), as single photon emitters at room temperature (Nat. Commun. 2021, 12, 2119), optical biosensors (Nat. Commun. 2024, 15, 706) or as fluorescent probes for in-vivo imaging in the second-biological window (NIR-II). However, obtaining luminescent defects with high brightness can be challenging with the current functionalization methods due to a small window of reaction conditions and the need for special chemicals (e.g., harmful diazonium salts). Here we report a novel method for introducing luminescent oxygen defects that only uses benign and inexpensive reactants. Sorted (6,5) SWCNTs in aqueous dispersion that are functionalized this way show bright defect emission at 1105 nm with a six times higher absolute photoluminescence quantum yield than the pristine nanotubes, reaching 3%. This functionalization can be performed within a wide range of reaction parameters and even with unsorted nanotube raw material at high concentrations, thus giving access to large amounts of brightly luminescent SWCNTs. The functionalization of biocompatible and ultra-short SWCNTs with these oxygen defects enables sufficiently bright emission for easy single-particle tracking in biological tissue.