Progress on quantum transport engineering in atomically precise anisotropic nanoporous graphene

Bottom-up on-surface synthesis has demonstrated an impressive capability to realize desired carbon nanomaterials with atomic precision, also referred to as carbon nanoarchitectures. By using chemically tailored organic building blocks, it is possible to obtain virtually any carbon nanoarchitecture, with equally tunable electronic and magnetic properties. Among all known carbon nanoarchitectures, graphene nanoribbons (GNRs) have become the most extensively studied for nanoelectronics, due to their conductive π-conjugated structure and semiconducting nature. In this review, we summarize the progress made on a particular type of nanoporous graphenes (NPGs), conceived as 2D arrays of laterally bonded GNRs. Due to their relative novelty, these GNR-based NPGs have not yet acquired the same global attention as their predecessors (GNRs). However, recent progress suggests that these nanomaterials may play a central role in future carbon nanoelectronics and spintronics. This is due in large part to the ability to fine tune, both by chemical design and by external means, the electronic coupling between neighbouring GNRs within the NPG, thereby enabling precise control over the anisotropic properties of these materials, as demonstrated by various theoretical studies. In this review, we summarize the different approaches that have been proposed to tune such inter-ribbon coupling and, thus, the anisotropy. Overall, these studies underscore the unique platform that GNR-based NPGs provide for tailoring quantum electronic properties and two-dimensional anisotropy. As the field progresses, this capability could be harnessed for targeted applications at the molecular scale or even the atomic scale.