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Linear electronic band dispersion and the associated Dirac physics has to date been limited to special-case materials, notably graphene and the surfaces of three-dimensional (3D) topological insulators. Here we report that it is possible to create two-dimensional fully conjugated polymer networks with corresponding conical valence and conduction bands and linear energy dispersion at the Fermi level. This is possible for a wide range of polymer types and connectors, resulting in a versatile new family of experimentally realisable materials with unique tuneable electronic properties. We demonstrate their stability on substrates and possibilities for doping and Dirac cone distortion. Notably, the cones can be maintained in 3D-layered crystals. Resembling covalent organic frameworks, these materials represent a potentially exciting new field combining the unique Dirac physics of graphene with the structural flexibility and design opportunities of organic-conjugated polymer chemistry.

International audienceDensity functional calculations are used to perform a systematic study of the effect of edge-functionalization on the structure and electronic properties of graphene nanoribbons (GNRs). −H, −F, −Cl, −Br, −S, −SH, and −OH edge-functionalization of armchair, zigzag, and reconstructed Klein-type GNRs was considered. The most energetically favorable edge structure varies depending on the choice of functional group. It is shown, for the first time, that reconstructed Klein-type GNRs are important stable configurations for several edge-functional groups. Band gaps using three different exchange-correlation functionals are calculated. The band gap for armchair GNRs can be tuned over a range of 1.2 eV by varying the edge-functional groups. In contrast, the band gaps of zigzag and reconstructed Klein edge GNRs are largely insensitive to the choice of edge-functional group, and ribbon width is instead the defining factor. Alternatively, the armchair GNR band gap can be controlled by varying the number of functional groups per opposing edge, altering the GNR "effective" width. Edge-functionalization design is an appropriate mechanism to tune the band gap of armchair GNRs

International audienceHydrogenated graphene edges are assumed to be either armchair, zigzag or a combination of the two. We show that the zigzag is not the most stable fully hydrogenated structure along the <2-1-10> direction. Instead hydrogenated Klein and reconstructed Klein based edges are found to be energetically more favourable, with stabilities approaching that of armchair edges. These new structures "unify" graphene edge topology, the most stable flat hydrogenated graphene edges always consisting of pairwise bonded C2H4 edge groups, irrespective the edge orientation. When edge rippling is included, CH3 edge groups are most stable. These new fundamental hydrogen terminated edges have important implications for graphene edge imaging and spectroscopy, as well as mechanisms for graphene growth, nanotube cutting, and nanoribbon formation and behaviour

A new modular approach to the smallest substituted cycloparaphenylenes (CPPs) is presented. This versatile method permits access to substituted CPPs, choosing the substituent at a late stage of the synthesis. Variously substituted [8]CPPs have been synthesized, and their properties analyzed. The structural characteristics of substituted CPPs are close to those of unsubstituted CPPs. However, their optoelectronic behavior differs remarkably due to the larger torsion angle between the phenyl units.

Carbonaceous presolar grains of supernovae origin have long been isolated and are determined to be the carrier of anomalous 22 Ne in ancient meteorites. That exotic 22 Ne is, in fact, the decay isotope of relatively short-lived 22 Na formed by explosive nucleosynthesis, and therefore, a selective and rapid Na physical trapping mechanism must take place during carbon condensation in supernova ejecta. Elucidation of the processes that trap Na and produce large carbon molecules should yield insight into carbon stardust enrichment and formation. Herein, we demonstrate that Na effectively nucleates formation of Na@C 60 and other metallofullerenes during carbon condensation under highly energetic conditions in oxygen-and hydrogen-rich environments. Thus, fundamental carbon chemistry that leads to trapping of Na is revealed, and should be directly applicable to gas-phase chemistry involving stellar environments, such as supernova ejecta. The results indicate that, in addition to empty fullerenes, metallofullerenes should be constituents of stellar/circumstellar and interstellar space. In addition, gas-phase reactions of fullerenes with polycyclic aromatic hydrocarbons are investigated to probe "build-up" and formation of carbon stardust, and provide insight into fullerene astrochemistry.

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