Optical Resolution of Single-Walled Carbon Nanotubes through Molecular Recognition with Chiral Diporphyrin Nanotweezers

Abstract

Single-walled carbon nanotubes (SWNTs) have either chiral or achiral form, and synthesized chiral SWNTs include both leftand right-handed structures in equal amounts. Recently, a racemic mixture was found to be resolved through molecular recognition with gable-type chiral diporphyrins, namely, nanotweezers. This novel separation method for SWNTs allowed optical resolution of SWNTs for the first time. The chiral nanotweezers consist of two chiral porphyrins and rigid spacer in between. Therefore, they have potential to discriminate not only the handedness but also the diameters or alignments of the hexagons of SWNTs. We have prepared the following three types of chiral nanotweezers; m-phenylene-, 2,6-pyridylene-, and 3,6-carbazolylene-bridged diporphyrins. In the extraction of SWNTs, different selectivities have been observed among the nanotweezers. This can be attributed to the differences in their structures; namely, the dihedral angles and the distance of the two porphyrins. In this review, we would like to discuss the relationship between the structures of the nanotweezers and the results of the optical and (n,m) enrichments of the extracted SWNTs.

Assignment of the Absolute‐Handedness Chirality of Single‐Walled Carbon Nanotubes by Using Organic Molecule Supramolecular Structures

“…Except for armchair and zigzag structures, which do not have non‐superimposable mirror images, all SWNT have handedness chirality. P (plus) and M (minus) terminology is used to define right‐ and left‐handed helical structures of SWNT, respectively (Figure a). This can be further explained using tube vector lines; these are represented by the ‘zigzag lines’ found on each SWNT using the arrows I, II, and III in Figure a.…”

“…This can be further explained using tube vector lines; these are represented by the ‘zigzag lines’ found on each SWNT using the arrows I, II, and III in Figure a. If two of these lines are rotated towards the right and the third line is rotated to the left, the chiral SWNT is known as the P type: Conversely, when the SWNT has two lines rotated to the left and the third is to the right, it is M type . Although the ( n,m ) indices of SWNT can be identified using spectroscopic techniques, such as UV/Vis, Raman, and photoluminescence (PL) spectroscopies; such kinds of techniques are difficult to use in the identification of the handedness chiralities, in which both P ‐ and M ‐SWNT enantiomers give the same results, in other words, clear experimental identification of handedness chiralities ( P and M ) of SWNT is yet to be established.…”

Single‐walled carbon nanotube absolute‐handedness chirality assignment confirmation using metalized porphyrin's supramolecular structures via STM imaging technique

“…3 We have observed various helical structures of Ni-BDP molecules on the tube surface in which the molecules form several wrapping patterns. This is due to the wide variety of (n,m) chiralities included in the SWNT samples used,[16d] eg, (9,6), (9,7), (8,7), (12,3), and (13,4). This can be clearly demonstrated in Figures 2 and S1.…”

“…7 The left-and right-handed helical structures of SWNTs can be defined using the M (minus) and P (plus) terminology, respectively. 3,8 Unlike the SWNT (n,m) chirality (which can be experimentally characterized via many spectroscopic techniques, eg, photoluminescence, UV-visible, and Raman spectroscopy 9 ), the SWNT absolute-handedness chirality is difficult to identify using these techniques because Pand M-SWNTs produce identical spectra. 3 Porphyrins and related compounds have attracted considerable attention because of their promising chemical, physical, and optoelectronic properties.…”

Resonance Raman Optical Activity of Single Walled Chiral Carbon Nanotubes

“…6 Various solutions for enrichment in a single enantiomer emerged only recently and are still actively investigated. [7][8][9] Techniques under current development exploit enantiomer specific interactions between a SWCNT and a carefully designed chiral bonding agent. 9,10 Chiral complexation were carried out with DNA strands, 11 chiral polymers, 12 nanotweezers 13,14 and chiral surfactants 15,16 and then standard separation ideas, chromatography, 11,17 extraction [12][13][14]18 and ultracentrifugation 15,16 yielded optically active SWCNT samples.…”