Graphenes as Potential Material for Electronics

Nonplanar aromatic compounds. 9. Synthesis, structure, and aromaticity of 1:2,13:14-dibenzo[2]paracyclo[2](2,7)- pyrenophane-1,13-diene

Pyrenophane (6) and an octaphenyl derivative (16) were synthesized using two different routes. Both cyclophanes contain a severely bent pyrene unit (6: theta = 93.6 degrees and 16: theta = 95.8 degrees , according to DFT-calculations (B3LYP/6-311G**)), which was generated at room temperature by a valence isomerization/dehydrogenation (VID) reaction. HOMA and NICS indicate 92-98% retention of aromaticity of the highly distorted pyrene systems compared to planar pyrene.

Self-organization of a discotic coordination complex bearing orthogonal discotic ligands

A new coordination complex that incorporates discotic ligands oriented orthogonally to a central discotic unit has been synthesized, and images of self-organized structures on highly oriented pyrolytic graphite have been obtained. Scanning tunneling microscopy images show that the combination of the orthogonally disposed discotic components results in significantly different self-organized structures compared to those of the ligand, which contains a single discotic unit.

Magnetism in graphene nanoislands

We study the magnetic properties of nanometer-sized graphene structures with triangular and hexagonal shapes terminated by zigzag edges. We discuss how the shape of the island, the imbalance in the number of atoms belonging to the two graphene sublattices, the existence of zero-energy states, and the total and local magnetic moment are intimately related. We consider electronic interactions both in a mean-field approximation of the one-orbital Hubbard model and with density functional calculations. Both descriptions yield values for the ground state total spin S consistent with Lieb's theorem for bipartite lattices. Triangles have a finite S for all sizes whereas hexagons have S=0 and develop local moments above a critical size of approximately 1.5 nm.

First principles study of magnetism in nanographenes

Magnetism in nanographenes [also known as polycyclic aromatic hydrocarbons (PAHs)] is studied with first principles density functional calculations. We find that an antiferromagnetic (AFM) phase appears as the PAH reaches a certain size. This AFM phase in PAHs has the same origin as the one in infinitely long zigzag-edged graphene nanoribbons, namely, from the localized electronic state at the zigzag edge. The smallest PAH still having an AFM ground state is identified. With increased length of the zigzag edge, PAHs approach an infinitely long ribbon in terms of (1) the energetic ordering and difference among the AFM, ferromagnetic, and nonmagnetic phases and (2) the average local magnetic moment at the zigzag edges. These PAHs serve as ideal targets for chemical synthesis of nanographenes that possess magnetic properties. Moreover, our calculations support the interpretation that experimentally observed magnetism in activated carbon fibers originates from the zigzag edges of the nanographenes.

Two-Dimensional Electronic Conjugation: Statics and Dynamics at Structural Domains Beyond Molecular Wires

Chemical architectures supporting a high degree of electronic conjugation serve as important functional components in devices and materials for advanced electronic and photonic applications. Increasing the spatial dimensionality of such constructs can fundamentally modify their optoelectronic properties and significantly alter intra- and intermolecular interactions that are crucial for understanding and controlling charge/energy-transfer processes. In this article, emerging design principles in the construction of well-defined conjugated platforms beyond molecular wires are highlighted. Both covalent and noncovalent approaches can be strategically employed to position one-dimensional (1D) substructures in a spatially well-defined manner in order to enhance both structural and functional complexity in a two-dimensional (2D) setting. A predictable and controllable switching mechanism can be designed and implemented with mobile 2D electronic conjugation that operates by correlated motions of inherently rigid 1D subunits. This emerging "dynamic" approach complements and challenges the prevailing "static" paradigm of conjugated chemical architectures.