Introducing the quantum defects into single-walled carbon nanotubes (SWNTs) enhances their photoluminescence (PL) with red-shifted peaks; however, the precise control of the chemical modification and PL wavelength remains difficult. In this work, the stepwise chemical functionalization of SWNTs was shown to be useful for controlling site-specific functionalization and PL, experimentally and theoretically. Dialkylated and hydroalkylated SWNTs were selectively synthesized using alkyllithium reagents, bromoalkane, and trifluoroacetic acid. The n Bu-SWNT- n Bu and n Bu-SWNT-H adducts of the (6,4), (6,5), (8,3), and (7,5) SWNTs that were separated using gel chromatography showed dominant E11 ** PL and E11* PL, respectively. The systematic assignments of the PL were performed based on the thermodynamic stability and transition energy of 1,2- and 1,4-adducts of SWNTs using density functional theory (DFT) and time-dependent DFT calculations. It was shown that the steric hindrance of the added group and the R value, that is, mod(n – m, 3) in an (n,m) chiral nanotube, are key factors that control the addition site and the magnitude of the local band gap.

The functionalization of single‐walled carbon nanotubes (SWNTs) is an effective method for controlling a local band gap, resulting in photoluminescence (PL) in the near‐infrared region. Herein, SWNTs were functionalized using a series of bromoalkanes and dibromoalkanes to evaluate the effects of their length on the nanotube PL properties. When bromoalkanes (CnH2n+1Br) or dibromoalkanes (CnH2nBr2) with tether lengths of six or more were utilized for six different semiconducting SWNTs, the obtained SWNT adducts exhibited two new PL peaks, whereas dibromoalkanes with tether lengths of 3–5 (CnH2nBr2: n=3–5) produced single peaks. Combined with theoretical calculations, the results suggested that the tether length of reagents changes the formation mechanism of functionalized adducts, that is, CnH2nBr2 (n=3–5) tends to result in kinetic products.