Stepwise Functionalization of Single-Walled Carbon Nanotubes with Subsequent Molecular Conversion to Control Photoluminescence Properties.

Functionalization of single-walled carbon nanotubes (SWNTs) has attracted interest because it alters the near-infrared (NIR) photoluminescence (PL) wavelength and emission efficiency. These modifications depend on the binding configuration and degree of functionalization. Excessive functionalization reduces the emission efficiency as the integrity of the conjugated p-system decreases, making controlling the degree of functionalization essential. Because the binding configurations and degree of functionalization are affected by the reagent structure, a stepwise approach combining functionalization reactions of SWNTs and subsequent reactions to introduce functional groups into the addenda could effectively control their PL properties and functionalities. We studied this approach by implementing the reductive alkylation of SWNTs using bromoalkanes with t-butyl carbamate (Boc)-protected amino groups and subsequent deprotection and amidation reactions. The reaction products were analyzed based on absorption, PL, and Raman spectroscopy and the Kaiser test. Depending on the structure of the reagent, deprotection and amidation reactions competed with the elimination reaction of addenda, changing the PL properties of the SWNTs. Furthermore, the elimination reaction was inhibited in the adducts functionalized with dibromoalkane with Boc-protected amino groups, demonstrating that the use of appropriate reagents enables molecular conversion of the functional groups of SWNT adducts without affecting their PL properties.