Graphene Nanoribbons Derived from Zigzag Edge-Encased Poly(para-2,9-dibenzo[bc,kl]coronenylene) Polymer Chains

Abstract

In this work, we demonstrate the bottom-up on-surface synthesis of poly­(para-dibenzo­[bc,kl]-coronenylene) (PPDBC), a zigzag edge-encased analog of poly­(para-phenylene) (PPP), and its lateral fusion into zigzag edge-extended graphene nanoribbons (zeeGNRs). Toward this end, we designed a dihalogenated di­(meta-xylyl)­anthracene monomer displaying strategic methyl groups at the substituted phenyl ring and investigated its applicability as precursor in the thermally induced surface-assisted polymerization and cyclodehydrogenation. The structure of the resulting zigzag edge-rich (70%) polymer PPDBC was unambiguously confirmed by scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM). Remarkably, by further thermal treatment at 450 °C two and three aligned PPDBC chains can be laterally fused into expanded zeeGNRs, with a ribbon width of nine (N = 9) up to 17 (N = 17) carbon atoms. Moreover, the resulting zeeGNRs exhibit a high ratio of zigzag (67%) vs armchair (25%) edge segments and feature electronic band gaps as low as 0.9 eV according to gaps quasiparticle calculations.

Modified Engineering of Graphene Nanoribbons Prepared via On‐Surface Synthesis

“…e) Synthetic route of zeeGNRs. Reproduced with permission . Copyright 2019, American Chemical Society.…”

“…It can be visually observed that the precursor directly determines the ribbons' periphery structure (cove edge). With precise design of the precursor, zigzag edge‐extended GNRs (zeeGNRs) as another novel structure (Figure e) were recently explored by Beyer et al Other than using one type of precursor, two or more kinds of building blocks can be used in combination to grow various GNR heterojunctions. Gröning et al used a single precursor and a combination of two precursors to prepare various types of GNRs (Figure f) .…”

On‐Surface Synthesis of NBN‐Doped Zigzag‐Edged Graphene Nanoribbons

“…Similar to NBN‐ZGNR1, the nitrogen and boron atoms were clearly unveiled in NBN‐ZGNR2 by nc‐AFM measurements (Figure f). Due to the NBN edge doping, these two GNRs featured stable zigzag edges in which no further reaction such as edge fusing was observed after thermal annealing, in contrast to the pristine carbon‐based ZGNRs …”

Chemical Synthesis at Surfaces with Atomic Precision: Taming Complexity and Perfection

“…Recently, new type zigzag edge‐extended GNRs with a width of 9 to 11 carbon atoms was derived from zigzag edge‐encased poly( para ‐2,9‐dibenzo[ bc , kl ]coronenylene) polymer chains. These GNRs exhibited a high ratio of zigzag (67 %) to armchair (25 %) edge segments . Furthermore, the addition of heteroatom dopants into the GNRs represents another efficient approach to modulate the band structure and electronic properties of the GNRs.…”