Fully cove-edged bilayer nanographene with parallel displaced stacking

Owing to the lack of precise atomic-level control offered by existing fabrication techniques over the edge structures in bilayer graphene, experimental studies on the edge effects in bilayer graphene structures have so far largely remained unexplored. In this study, two fully cove-edged bilayer nanographenes (CBGs) are synthesized via organic synthesis approach. One of the prepared CBGs contains a cavity defect. The bilayer stacked structures of CBGs are unambiguously characterized. Two CBGs exhibit a parallel displaced stacking arrangement with tunable interlayer overlapping, which is controlled by the steric hindrance at the cove edges. The different interlayer overlapping results in different interlayer electronic coupling. The decrease in the energy gaps is linked to the cove edges, which leads to a redshift in the optical absorption and emission spectra of the CBGs, which is further used for the NIR-II bioimaging.