The adsorption of the organic donor molecules tetrakis(dimethylamino)ethylene (TDAE) and cobaltocene (CoCp(2)) on high-pressure CO decomposition (HiPco) single-walled carbon nanotubes (SWNTs) is investigated using density functional theory (DFT), optical absorption, and Raman spectra methods. The selective reduction of SWNTs according to the electronic type and diameter of SWNTs is revealed. The reduction rate decreases in the order: metallic SWNTs >or= large-diameter semiconducting SWNTs > small-diameter semiconducting SWNTs.