Regioselective On-Surface Synthesis of [3]Triangulene Graphene Nanoribbons
Michael C. Daugherty, Peter H. Jacobse, Jingwei Jiang, Joaquim Jornet-Somoza, Reis Dorit, Ziyi Wang, Jiaming Lu, Ryan D. McCurdy, Weichen Tang, Ángel Rubio, Steven G. Louie, Michael F. Crommie, Felix R. Fischer
Abstract
High Resolution Image Download MS PowerPoint Slide The integration of low-energy states into bottom-up engineered graphene nanoribbons (GNRs) is a robust strategy for realizing materials with tailored electronic band structure for nanoelectronics. Low-energy zero-modes (ZMs) can be introduced into nanographenes (NGs) by creating an imbalance between the two sublattices of graphene. This phenomenon is exemplified by the family of [ n ]triangulenes ( n ∈ N ). Here, we demonstrate the synthesis of [3]triangulene-GNRs, a regioregular one-dimensional (1D) chain of [3]triangulenes linked by five-membered rings. Hybridization between ZMs on adjacent [3]triangulenes leads to the emergence of a narrow band gap, E g,exp ∼ 0.7 eV, and topological end states that are experimentally verified using scanning tunneling spectroscopy. Tight-binding and first-principles density functional theory calculations within the local density approximation corroborate our experimental observations. Our synthetic design takes advantage of a selective on-surface head-to-tail coupling of monomer building blocks enabling the regioselective synthesis of [3]triangulene-GNRs. Detailed ab initio theory provides insights into the mechanism of on-surface radical polymerization, revealing the pivotal role of Au–C bond formation/breakage in driving selectivity.