Optical and Vibrational Properties of Toroidal Carbon Nanotubes

Highly Contorted Rigid Nitrogen-Rich Nanographene with Four Heptagons

Nucleophilic substitution of 9,10-dichlorooctafluoroanthracene with 3,4-diethylpyrrole and subsequent Scholl reaction give the annularly fused decapyrrollyl anthracene. Single crystal X-ray analysis revealed a highly contorted geometry induced by a combination of adjacent heptagons, forming a unique 7-7-6-7-7 topology. The end-to-end twist angle along the acene moiety is 90°. Cyclic voltammetry studies reveal 6-electron oxidation waves. Density functional theory calculations provided further insights into the aromaticity and electronic properties of this highly twisted, nitrogen-rich nanographene. The structural rigidity and high racemization energy barrier have been studied theoretically and experimentally by VT-NMR.

Folding of fluorinated oligoarylenes into non-alternant PAHs with various topological shapes

An unprecedented [6]helicene's cavity closure indicating the possibility of introducing seven-membered rings via alumina-mediated C–F activation is shown.

Toward Negatively Curved Carbons

Negatively curved carbons are theoretical carbon allotropes as proposed by embedding heptagons or octagons in a graphitic lattice. Unlike five-membered rings in fullerenes, which induce positive curvature, the seven- or eight-membered rings induce negative curvature, giving rise to a variety of esthetic carbon nanostructures known as Mackay crystals or carbon schwarzites. In addition, hypothetical toroidal carbon nanotubes consisting of five-, six-, and seven-membered rings present positive curvature on the outside and negative curvature on the inside of the torus. These carbon allotropes with negative curvature are predicted to have interesting properties and potential applications on the basis of computational studies but are yet to be synthesized. A promising bottom-up approach to these intriguing but still imaginary carbon structures is organic synthesis of negatively curved polycyclic arenes, which are also known as negatively curved nanographenes. They not only are segments of negatively curved carbon allotropes containing important structural information but also can in principle be used as templates or monomer units for the synthesis of carbon schwarzites and toroidal carbon nanotubes. This Account describes research on the design, synthesis, structure, stereochemical dynamics, and properties of negatively curved nanographenes, with emphasis on our efforts in this field. In our designs of negatively curved nanographenes, a few heptagon- or octagon-embedded π systems were employed as basic structural units, including [7]circulene, heptagon-embedded hexa- peri-benzocoronene, tetrabenzodipleiadiene, and [8]circulene. They present a saddle-shaped geometry and consist of a relatively small number of sp² carbon atoms. By expanding or connecting these structural units, we designed and synthesized larger negatively curved nanographenes consisting of up to 96 sp² carbon atoms. A method of key importance in the synthesis of negatively curved nanographenes is the Scholl reaction, which enables the formation of multiple carbon-carbon bonds in a single step by intramolecular oxidative cyclodehydrogenation. The unique structures of negatively curved nanographenes were studied by experimental and computational methods. In particular, X-ray crystallography of single crystals revealed remarkably curved π faces accompanied by severe out-of-plane deformation of benzenoid rings, which sheds light on the limit of π bonds and the aromaticity of polycycles. As found mainly from calculations, the flexible polycyclic frameworks of negatively curved nanographenes are associated with stereochemical dynamics that is not available for planar polycyclic aromatics. In addition, some negatively curved nanographenes have been found to function as organic semiconductors in the solid state. We envision that the study of negatively curved nanographenes will serve as an important initial step toward the eventual synthesis of new carbon allotropes with negative curvature and new frontiers of nanocarbon materials.

Synthesis, Structure, and Properties of Tetrabenzo[7]circulene

Tetrabenzo[7]circulene, a new member of aromatic saddles, was conveniently synthesized from 2-(1-naphthoyl)benzoic acid with the seven-membered ring constructed at an early stage of the synthesis. This method, upon minor modification, was also useful for synthesis of thiophene-annulated [7]circulenes. The structures of tetrabenzo[7]circulene and [7]circulene were compared in terms of symmetry, flexibility, and curvature on the basis of DFT calculations and X-ray crystallography. It was also found that tetrabenzo[7]circulene functioned as a p-type semiconductor in thin-film transistors and cocrystallized with C₆₀.

Chirality in curved polyaromatic systems

Chiral non-planar polyaromatic systems that display zero, positive or negative Gaussian curvature are analysed and their potential to ‘encode’ chirality of larger sp²-carbon allotropes is evaluated. Shown is a hypothetical peanut-shaped carbon allotrope, where helical chirality results from the interplay of various curvature types.

From tetrabenzoheptafulvalene to sp2 carbon nano-rings

A new kind of sp² carbon nano-rings containing a heptagon and an octagon was synthesized by taking advantage of the “C” shape of syn-tetrabenzoheptafulvalene.

Symmetry groups associated with tilings on a flat torus

This work investigates symmetry and color symmetry properties of Kepler, Heesch and Laves tilings embedded on a flat torus and their geometric realizations as tilings on a round torus in Euclidean 3-space. The symmetry group of the tiling on the round torus is determined by analyzing relevant symmetries of the planar tiling that are transformed to axial symmetries of the three-dimensional tiling. The focus on studying tilings on a round torus is motivated by applications in the geometric modeling of nanotori and the determination of their symmetry groups.

Synthesis and non-covalent functionalization of carbon nanotubes rings: new nanomaterials with lectin affinity

We present a mild and practical carbon nanotubes rings (CNRs) synthesis from non-covalent functionalized and water-soluble linear single-wall carbon nanotubes. The hemi-micellar-supramolecular self-organization of lactose-based glycolipid 1 on the ring surface, followed by photo-polymerization of the diacetylenic function triggered by UV light afforded the first water-soluble and biocompatible CNRs. The obtained donut-like nanoconstructs expose a high density of lactose moieties on their surface, and are able to engage specific interactions with Arachis hypogea lectin similar to glycoconjugates on the cell membrane.