Controlling Near-Infrared Photoluminescence Properties of Single-Walled Carbon Nanotubes by Substituent Effect in Stepwise Chemical Functionalization

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 nBu-SWNT-nBu and nBu-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.