Self-assembled graphitic nanotubes with one-handed helical arrays of a chiral amphiphilic molecular graphene

Abstract

Self-assembly of a Gemini-shaped, chiral amphiphilic hexa-perihexabenzocoronene having two chiral oxyalkylene side chains, along with two lipophilic side chains, yields graphitic nanotubes with one-handed helical chirality. The nanotubes are characterized by an extremely high aspect ratio of >1,000 and have a uniform diameter of 20 nm and a wall thickness of 3 nm. The nanotubes with right-and left-handed helical senses were obtained from the (S)-and (R)-enantiomers of the amphiphile, respectively, due to an efficient translation of point chirality into supramolecular helical chirality. The (S)-and (R)-enantiomers coassemble at varying mole ratios to give nanotubes, whose circular dichroism profiles are almost unchanged over a wide range of the enantiomeric excess of the amphiphile (100 -20%). The high level of chirality amplification thus observed indicates a long-range cooperativity in the selfassembling process. In sharp contrast, a hexabenzocoronene amphiphile with chiral lipophilic side chains did not form nanotubular assemblies. The present work demonstrates the majority rule in noncovalent systems and also may provide a synthetic strategy toward realization of molecular solenoids. chirality ͉ self-assembly H elicity is one of the most essential structural elements for certain biomolecules such as peptides and DNA. The prominent functions of these biological components have motivated chemists to design artificial helical architectures (1-8), which can be used for a variety of applications such as chiral separation (9, 10) and sensing (11-15), asymmetric synthesis (16), liquid crystals (17-19), nonlinear optics (20, 21), and so forth. Recently, a hot issue of chirality has emerged in relation to the helicity of the hexagonal carbon lattice in carbon nanotubes, because it determines the conductive properties of carbon nanotubes (22-24). Conductive polymers with helical architectures (25) also have attracted attention in view of the concept of molecular solenoids (26,27), although this concept has yet been a dream of scientists, because there are no molecular objects that fulfill certain requisites for conductivity and helicity. Here, we report an example of conductive tubular objects consisting of one-handed helical arrays of a -stacked chiral molecular graphene. Self-assembly of hexa-peri-hexabenzocoronene (HBC) derivatives to form discotic liquid crystals and nanofibers has been studied extensively by Müllen and coworkers (28,29). We recently found that an amphiphilic HBC derivative (1) (Fig. 1) self-assembles in polar organic solvents such as tetrahydrofuran (THF) to give graphitic nanotubes, whose wall consists of a bilayer tape formed from bilaterally coupled columns of -stacked HBC units (30). In the course of this work, we have noticed that the self-assembly of 1, although achiral, gives a mixture of coiled and tubular assemblies under certain conditions, suggesting that the tubular objects also bear a helical structural element. This observation prompted us to design chiral HBC amphiphiles 2 and 3 (Fi...

Principles of self-assembly of helical pores from dendritic dipeptides

“…The helicity of the columns selfassembled from achiral dendritic alcohols provides definitive demonstration for our previous hypothesis that the helicity of the dendritic dipeptides is induced by their achiral dendrons (15,16). This self-assembly system relates to other processes in which a stereocenter selects the twist sense of a racemic helical structure (10,23,24) and is in agreement with the principles elaborated by Green et al (25). However, it differs from those in which a stereocenter induces helicity in an achiral nonhelical system (26).…”

Self‐assembled organic nanotubes: Toward attoliter chemistry

“…20 Those nanotubes are of great interest in terms of possibly sharing the properties of CNT and LNT. [24][25][26] …”

Possible One-Dimensional Helical Conductor: Hexa-peri-hexabenzocoronene Nanotube

“…[1][2][3][4] A hot tetrahydrofuran solution (50 C) of HBC molecules was cooled down to 25 C. For fibers, large bundles of nanotubes were obtained after three weeks. A glass hook was dipped into this suspension to collect the nanotube bundles.…”

“…1). [1][2][3] In the case of the ordinal carbon nanotube, the conjugated two-dimensional molecular wave-function is spread on the surfaces of the nanotubes. However, in the case of the HBC nanotubes, the -conjugated columns stack along the one-dimensional chain direction.…”