Mechanically Interlocked Single‐Wall Carbon Nanotubes

Abstract

Extensive research has been devoted to the chemical manipulation of carbon nanotubes. The attachment of molecular fragments through covalent-bond formation produces kinetically stable products, but implies the saturation of some of the C-C double bonds of the nanotubes. Supramolecular modification maintains the structure of the SWNTs but yields labile species. Herein, we present a strategy for the synthesis of mechanically interlocked derivatives of SWNTs (MINTs). In the key rotaxane-forming step, we employed macrocycle precursors equipped with two π-extended tetrathiafulvalene SWNT recognition units and terminated with bisalkenes that were closed around the nanotubes through ring-closing metathesis (RCM). The mechanically interlocked nature of the derivatives was probed by analytical, spectroscopic, and microscopic techniques, as well as by appropriate control experiments. Individual macrocycles were observed by HR STEM to circumscribe the nanotubes.

The mechanical bond on carbon nanotubes: diameter-selective functionalization and effects on physical properties

“…58, 60 The individual emission spectra, shown in the Supporting Information, clearly demonstrate the selective fluorescence quenching of smaller diameter SWNTs such as (6,5), (8,3), and (7,5), when compared to the slightly larger (8,4) and (7,6), in line with our observations in absorption. Given the similar electronic nature of these chiralities, this selective quenching most likely stems from a higher degree of functionalization with macrocycle 2.…”

“…59, 60 The MINT(6,5)-2 spectrum failed to exhibit major changes as far as absorption maxima are concerned. Nevertheless, a slight broadening as well as an overall intensity decrease of the absorption features for MINT(6,5)-2 point to weak electronic interactions between the exTTF macrocycles and SWNTs in the ground state.…”

“…60 Very briefly, we exploited the positive exTTF-SWNT interaction 61 to template the ring closing metathesis of 1 around the nanotubes, to form MINTs (Figure 1). Unreacted 1, non-threaded 2, linear oligomers of 1, formed in situ under the RCM reaction conditions, catalyst, etc.…”

“…This observation indicates very weak charge-transfer interactions between electron donating exTTF and SWNT in the ground state, and is in accordance with our previous observations. 60 The size selectivity was investigated by careful analysis of the low frequency radial breathing mode (RBM) bands ( Figure 5, bottom part). In both samples, three RBM features, at 268, 311, and 331 cm -1 originating from (7,6), (6,5), and (6,4)-SWNTs, respectively, were detected.…”

“…In particular, we described the synthesis of rotaxane-type derivatives of SWNTs -the first example of mechanically interlocked SWNTs (MINTs). [58][59][60] With synthetic routes towards MINTs established, we decided to investigate the consequences of the mechanical bond on the properties of both SWNT and macrocycle(s). Here, we report that the MINT-forming reaction proceeds in a chirality-selective fashion, favoring functionalization of smaller diameter SWNTs.…”