Bandgap Engineering of Graphene Nanoribbon via High-Pressure Topochemical Synthesis.

Graphene nanoribbons (GNRs) have attracted broad attention for their potential application in nanoelectronics. The electronic properties of the GNRs are closely related to their chemical structure like width, edge, terminating and hetero atoms, etc., and widely applied synthetic methods for the scalable synthesis of specific GNRs with atom-scale precision are urgently required. Here, we found that the stoichiometric and ordered positioning of N and sp3-CH in 8-armchair-GNR ([8]-AGNR) effectively modifies their bandgap in a large range of 0-2.85 eV by theoretical calculations. Employing our recent-developed high-pressure topochemical dehydro-Diels-Alder polymerization, three of these [8]-AGNRs were synthesized successfully in their bulk phase starting from crystalline dipyridinyl/dipyrimidinyl butadiynes, with the maximum nitrogen content of 27% in mass. The structures of these GNRs were demonstrated by spectroscopy, diffraction, transmission electron microscope, pair distribution function, and solid-state nuclear magnetic resonance methods. UV-vis-NIR diffuse reflectance spectra clearly evidenced the precise tuning of the electronic structures in these N and CH substituted [8]-AGNRs. Our work shows great versatility of this high-pressure topochemical synthetic strategy in synthesizing GNRs with site-specific N and sp3-CH substitutions. This strategy can also be applied to synthesizing more structure-specific carbon nano-materials.