Guiding the geometry of graphene nanoribbon heterojunction via surface-adsorbed 10,10'-dibromo-9,9'-bianthryl.

Using 10,10'-dibromo-9,9'-biphenanthryl (DBBA) as a precursor, graphene nanoribbon (GNR) heterojunctions were synthesized on metal surfaces. On the Cu(110) surface, the strong interaction between DBBA molecules and the substrate limited the reaction pathway, resulting exclusively in the formation of graphene quantum dots via dehydrogenative cyclization. On Au(111), DBBA molecules underwent polymerization at elevated temperatures, yielding 7-atom-wide armchair GNRs (7aGNRs). These 7aGNRs could be further transformed into wider nanoribbons, such as 14aGNRs and 21aGNRs, through additional cyclization processes. Notably, by reducing the surface density of DBBA, unique heterostructures, including Y-type and T-type GNRs, were successfully fabricated. The T-type GNRs exhibited asymmetric heterojunctions, which provide a promising platform for engineering tunable bandgaps in GNRs. This study highlights precursor-molecule-substrate interactions in controlling GNR synthesis, advancing tailored graphene-based materials.