Extraction of carbon nanotubes with porphyrin- and pyrene-based nanotweezers and nanocalipers: Insight from the association constants

Strong interaction between porphyrin and nanocarbons including carbon nanotubes (CNTs) has been utilized to form stable complexes between them. We have applied the stable complex of CNTs with V- and U-shaped porphyrins and pyrenes, designated as nanotweezers and nanocalipers respectively, to separation of CNTs through their extraction to liquid phase. In order to know more about the CNT complex in liquid phase, we determined the association constants and the extraction ability of the host molecules, porphyrins, pyrenes, porphyrin- and pyrene-based nanotweezers and nanocalipers, to single-walled carbon nanotubes (SWNTs). As we expected, the order of the association constant is nanocalipers > nanotweezers > monoporphyrins > monopyrenes in the host molecules. The extraction ability of these host molecules is roughly proportional to the order of the association constants, but mismatching of the cavity size of the host and the diameter of CNTs is considered to become more apparant in liquid phase than in solid phase, destabilizing the complex in liquid phase and lowering the extraction ability.