Syntheses and Characterizations of Functional Polycyclic Aromatic Hydrocarbons and Graphene Nanoribbons

Abstract

Abstract In contrast to zero-bandgap graphene, nanostructures of graphene, such as graphene quantum dots (GQDs) and graphene nanoribbons (GNRs) have open bandgaps due to the quantum confinement effect, and are thus highly interesting for semiconductor applications, for example in nanoelectronics and optoelectronics. While conventional methods cannot provide GQDs and GNRs with chemically precise structures, large polycyclic aromatic hydrocarbon (PAH) molecules can be regarded as atomically precise GQDs. Moreover, extension of the PAH synthesis can lead to GNRs with well-defined chemical structures. In this account, we summarize our recent achievements in our synthetic exploration of PAHs and GNRs with novel structures and properties. For example, we have developed new PAHs having zigzag edges, such as dibenzo[hi,st]ovalene derivatives with strong red luminescence and stimulated emission, which are promising for light-emitting devices and bioimaging applications. We have also accomplished a synthesis of magnetic GNRs through edge functionalization with organic radicals, which can be interesting for spintronic as well as quantum computing applications. Moreover, incorporation of zigzag edges in GNR structures, through on-surface syntheses under ultrahigh (UHV) vacuum conditions, allowed for significant modulations of the electronic structures of GNRs, leading to the emergence of topological quantum phases. On the other hand, we have also explored on-surface synthesis of GNRs without UHV, namely using a setup for chemical vapor deposition (CVD). Scalable fabrication of GNR films could thus be achieved on gold on mica substrates, which could be integrated into field-effect transistor devices. These results highlight the importance of developing novel PAHs and GNRs and their potentials for various applications, including quantum technologies, energy and optoelectronic devices, and bioimaging.