(Invited) Towards Understanding the Competition of Electron and Energy Transfer in Nanographene

Abstract

Graphene has captured the imagination of researchers around the world due to its groundbreaking chemical and physical properties. Opening a band gap in graphene must be achieved without, however, compromising its exceptional properties as they are of paramount importance for its use in electronic devices. Notable is the fact that the band gap design in graphene is typically carried out by either chemical or physical methodologies. Chemical modification of graphene is mostly centered around “top-down” or “bottom-up” approaches. The earlier alters, nevertheless, the graphene lattice and, as a consequence, poorly defined structures emerge. The latter by means of, for example, organic synthesis offers a wide palette of tools to control sizes as well as geometries of the resulting “molecular” nanographenes with atomic precision. It allows the fabrication of uniform and well-defined molecular structures. Such “molecular” nanographenes are compelling choices for “on demand” molecular electronics, photovoltaic applications, hydrogen storage, and sensing. In recent years, two main strategies have been developed to fabricate “molecular” nanographenes of defined chemical structures. It is, on one hand, oxidative cyclodehydrogenation of custom-made polycyclic aromatic hydrocarbons (PAHs) and, on the other hand, on-surface cyclodehydrogenation, which enabled the preparation of atomically precise “molecular” nanographenes. To this end, the 13 fused-benzene rings of hexa- peri -hexabenzocoronene (HBC), which are arranged in a 2D disk-shaped fashion, render HBCs the smallest “molecular” nanographenes.