Swnt-Sorting with a Removable Solubilizer Based on Dynamic Supramolecular Coordination Chemistry

Highly pure semiconducting single-walled carbon nanotubes (SWNTs) are essential for the next generation of electronic devices, such as field-effect transistors and photovoltaic applications, but contamination by metallic-SWNTs reduces the efficiency of their associated devices. Polyfluorene-based copolymers (PFOs)^{1, 2} have been intensively studied because they dissolve/extract only sem-SWNTs in toluene by a simple sonication method. We have previously demonstrated a rational method for the selective extraction of a specific chirality of the sem-(n,m) SWNTs using a series of systematically designed fluorene-based copolymers^3-4. Moreover, we revealed that the PFO copolymers with a bulky optically active moiety could separate the right- and left-handed sem-SWNTs⁵. However, there are several serious problems when using PFOs; that is, difficulty in the removal of the wrapped PFOs from the SWNTs/PFO composites^{6, 7} as well as their low extraction efficiency from the as-produced SWNTs^{1, 2}.

     Here we report a simple and efficient method for the separation of semiconducting- and metallic-SWNTs based on supramolecular complex chemistry.⁸ We describe the synthesis of metal-coordination polymers (CP-M) composed of a fluorene-bridged bisphenanthroline ligand and metal ions. Based on a difference in the ‘solubility product’ of CP-M-solubilized semiconducting-SWNTs and metallic-SWNTs, we readily separated semiconducting-SWNTs. Furthermore, the CP-M polymers on the SWNTs were simply removed by adding a protic acid and inducing depolymerization to the monomer components. We also carried out molecular mechanics calculations to reveal the difference of binding and wrapping mode between CP-M/semiconducting-SWNTs and CP-M/metallic-SWNTs.

     This study opens a new stage for the use of such highly pure semiconducting-SWNTs in many possible applications.

 

References

[1] Chen, F., Wang, B., Chen, Y., Li, L.-J. Nano Lett. 7, 3013–3017 (2007).

[2] Nish, A., Hwang, J., Doig, J., Nicholas, R. Nature Nanotech. 2, 640-646 (2007).

[3] Ozawa, H. et al. J. Am. Chem. Soc. 133, 2651–2657 (2011).

[4] Ozawa, H., Ide, N., Fujigaya, T., Niidome, Y., Nakashima, N. Chem. Lett. 40, 239–241 (2011).

[5] Akazaki, K., Toshimitsu, F., Ozawa, H., Fujigaya, T., Nakashima, N. J. Am. Chem. Soc. 134, 12700–12707 (2012).

[6]  Izard, N. et al., App. Phys. Lett. 92, 243112 (2008).

[7] Jakubka, F. et al., ACS Macro Lett. 1, 815–819 (2012).

[8] Toshimitsu, F., Nakashima, N. Nature Comm., 2014, 5, art no. 5041.