Mixed-surfactant gating of aryl diazonium quantum defect formation in single-walled carbon nanotubes

Aryl diazonium chemistry is widely used to introduce luminescent sp³ quantum defects into single-walled carbon nanotubes (SWCNTs) for imaging, sensing, and photonic applications. However, controlling the extent of functionalization is nontrivial because excessive diazonium functionalization can disrupt the SWCNT sp² carbon network, leading to substantial loss of its characteristic optical absorption. Here, we show that mixed sodium dodecyl sulfate/sodium deoxycholate (SDS/DOC) surfactant coronas provide a simple way to regulate aryl diazonium access to the SWCNT sidewall. In DOC-only SWCNT dispersions, even 0.010% (m/V) DOC suppressed detectable aryl diazonium-induced defect formation, whereas SDS-only dispersions permitted rapid functionalization. By systematically varying the SDS/DOC composition, we identified a reaction window of ∼0.008 to 0.050% (m/V) DOC at 0.857% (m/V) SDS and 2.35 μM 4-nitrobenzenediazonium tetrafluoroborate that maximizes the brightening factor (integrated defect photoluminescence (PL) relative to pristine E₁₁ PL) while reducing E₁₁ absorption loss relative to SDS-only dispersions. These results support a mixed-surfactant gating model in which DOC protects the nanotube surface, while SDS-rich or less-protected regions permit diazonium adsorption and defect formation. Mixed-surfactant engineering therefore offers a practical strategy for tuning quantum defect formation in SWCNTs.