Multiproperty Atomistic Characterization of a Synthesized Pyrazinic Nitrogen-Doped Porous Armchair Graphene Nanoribbon

RESUMO

Graphene nanoribbons (GNRs) obtained by on-surface synthesis combine a width-controlled band gap with atomic precision, making chemical decoration of their edges and interiors a practical route to designed electronic and optical behavior. Ullmann coupling of a phenazine-bearing precursor yields a nine-atom-wide armchair ribbon that is periodically perforated and carries two two-coordinated nitrogen atoms at every pore rim. Here we characterize this ribbon across the properties relevant to device operation, alongside the pristine and undoped porous ribbon, disentangling the roles of pore formation and nitrogen incorporation. Perforation primarily governs mechanical and thermal response, whereas nitrogen substitution predominantly controls electronic and optical properties. Perforation removes the atomic row carrying frontier states, opening the gap into the range measured by tunneling spectroscopy while substantially reducing stiffness and thermal conductivity. Substitution leaves the mechanical response essentially unchanged and contributes a secondary conductivity reduction through phonon spectrum reweighting. Its primary effect is electronic: it selectively narrows the conduction band, binds the lowest exciton by 414 meV, and displaces the absorption edge into the red. The effective phonon mean free path we obtain, 9.9 nm, matches the length to which the synthesis presently limits these ribbons, placing reported samples at the ballistic-to-diffusive crossover. Adsorption on Au(111), Ag(111), and Cu(111) is energetically nearly indistinguishable and remains van der Waals in character, accounting for the substrate tolerance observed experimentally. Finally, graphitic rather than pyrazinic nitrogen would make the ribbon metallic, except when two atoms occupy pore-rim sites, yielding a ferromagnetic semiconducting state having a magnetic moment of 2 mu_B per unit cell.