Tuning the band structure of chiral Graphene Nanoribbons by functionalized edge groups

Graphene nanoribbons (GNRs) have become nanostructured materials of remarkable interest mainly due to the presence of an energy gap, boosting their possible applications in semiconductor technology with respect to the gapless graphene. The great advances achieved during the last decade in the bottom-up synthesis methodologies allow for the defect-free synthesis of GNRs, a key step for unraveling their innate electronic structure and for their posterior use in applications. Several efforts have been recently focused on tuning the electronic structure of GNRs by doping their carbon skeleton with different atoms like nitrogen, sulfur, boron, etc. Recently, Carbonell-Sanromà and co-workers followed a new approach by covalently bonding cyano groups at the external edges of armchair graphene ribbons while preserving the internal carbon structure, observing a rigid shifting of the frontier molecular bands defining the electronic band gap of the ribbons. Following this line, here we tune the recently reported electronic structure of (3,1)-chiral GRNs by adding two functional groups with opposite electronic character: nitro (NO2) and amino (NH2) groups, the former (latter) being a well-known electron-withdrawing (donor) group.