Functionalization of single-walled carbon nanotubes (SWCNTs) 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 π system decreases; thus, controlling the degree of functionalization is essential. Because the binding configurations and degree of functionalization are affected by the reagent structure, a stepwise approach combining SWCNTs functionalization 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 SWCNTs by 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, altering the PL properties of the SWCNTs. Furthermore, the elimination reaction was inhibited in the adducts functionalized using dibromoalkane with Boc-protected amino groups, demonstrating that the use of appropriate reagents enables the molecular conversion of the functional groups of SWCNT adducts without affecting their PL properties.
Keywords: amines; fluorescence; nanotubes; near-infrared; protecting groups.
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