Alkane Filled Single-Wall Carbon Nanotubes: Endohedral Volume Control for Improved Nanotube Properties

Abstract

Liquid-phase processing of single-wall carbon nanotubes (SWCNTs) generally results in the exposure of their core to the environment (opening) due to the energy input necessary for purification and solubilization, and this often affects the SWCNT properties [1-3]. For instance, for aqueous processing, SWCNTs are routinely getting filled with water, which leads to significant redshifts to, and inhomogeneous broadening of, the electronic transitions of the SWCNTs, as well as a substantial decrease of their fluorescence quantum efficiency [1]. Selection of (remaining) empty (end-capped) SWCNTs to avoid these detrimental effects is possible by means of ultracentrifugation, but is a natively low yield process [4]. In this work, adverse filling is prevented by intentionally prefilling the SWCNTs with alkanes, serving as a passive and highly homogeneous spacer. In contrast to water and other encountered fillants, the alkane core is of low dielectric nature and therefore only weakly affects the electronic structure of the SWCNTs, and hence effectively simulates empty core conditions. This yields highly resolved optical spectra with strongly shifted peak positions compared to water filled SWCNTs (see Figure 1), and fluorescence efficiencies approaching those of empty SWCNTs. It is demonstrated that this can be realized using a wide variety of linear as well as cyclic alkanes, in combination with various SWCNT materials having very different diameter distributions.